THE GEOLOGY OF DELAWARE*
DURING the years 1837 and 1838, Prof. Jas C. Booth, in accordance with an act of the State Legislature, made a geological survey of Delaware, the results of which were published in a report that appeared in 1841. This old memoir is of great value, both from the accuracy of the author's observations and his minute attention to detail; we cannot, therefore, expect to take anything from the character of this work, our aim being to so completely reconstruct our geology as to bring it into sympathy with results in adjacent States.
The formation represented within the bounds of the State are Archean, Cretaceous, Tertiary and Quaternary. The relations and positions of the several divisions of these formations are represented in the accompanying table, also the thickness of each. It will be understood that the formation oldest in age and order of deposition is placed at the bottom.
The geology of the State of Delaware is comparatively simple. The oldest Archean rocks cover all that portion of the State which lies to the north of the Philadelphia, Wilmington and Baltimore Railroad, where they are tilted at high angles, contorted and overthrown The region is one of great interest, and offers to the field geologist problems of such moment as to make it a classic field in American geology Resting upon the eroded edges of the Azoic rocks are successive series of plastic clays, sand marls and green sands, of Cretaceous age, which form quite uniform strata dipping at a low angle to the southeast. This belt, having a width of about eighteen miles, extends from the Archean hills to the latitude of Noxontown mill pond, just south of Middletown. The Cretaceous is succeeded by a stratum of white or lead colored clay having a thickness of ten to twenty feet.
This continues as far south as Murderkill Creek, and from fossiliferous evidence is probably Miocene. South of Murderkill Creek, the Miocene is succeeded by three to ten feet of light or dark blue clay, beneath which is a uniform stratum of fine white glass sand of at least forty feet in thickness. That all the State south of Murderkill is later Pliocene rather than Modern, as the older writers have claimed, has, we think, been well demonstrated. All the beds of the Tertiary lie in a nearly horizontal position, dipping at a still lower angle than the Cretaceous, and probably unconformable to the same.
Covering all of the foregoing formations, and reaching up the flanks of the Azoic hills to the height of two hundred feet or more above tide is a layer of sand and gravel, which to the north is of a coarse red nature, and to the south is fine and white. These gravels are of Quaternary age, and have been styled by the author the Delaware Gravels and Estuary Sands, respectively. Along the river and bay shores is also the belt of bog clay, which is modern, and of more recent origin than the Gravels.
THE ARCHEAN. Generally speaking, the southern line of the Azoic or Archean rocks is the limit of the "highlands," but in certain places they extend well into more level regions. Beginning with a point upon the Maryland boundary, a little north of where the latter is cut by the Mason and Dixon line, the limit of the rocks runs in a northeast direction, cutting through the western end of Newark, and following the northern boundary of the town. Thence it runs close to the south shore of White Clay Creek to a distance of two miles beyond Roseville, where it makes an abrupt bend to the north, until at Stanton the rocks cease to be found. A mile back of the railway station, they again appear, continuing to a point about a mile back of Newport, where their course runs slightly to the southeast, crossing the Wilmington turnpike just before it is intersected by the Wilmington Northern Railroad; thence it follows the turnpike through the southern half of the city, when it turns abruptly south to the river.
The character of the country covered by the Archean rocks is distinctly hilly, and stands in strong contrast to the low-lying region to the south. The rocks, however, are too uniform in texture and structure to cause marked topographic outlines. The region is rather rolling, or the hills low and undulating, between which are corresponding bowl shaped depressions. The elevation of this highland region varies between two hundred and three hundred and fifty feet above tide, gradually increasing to the north.
The Archean area of the State can be divided into two nearly equal areas. First, a southern club-shaped area of eruptive gabbros and hyperites with associated amphibole rocks, and Second, an upper elliptical area of softer micaceous gneisses and schists.
Almost the whole of Brandywine Hundred, and the southern half of Christiana Hundred are covered by the rocks of the first class. To the west of Brandywine Springs these rocks, however, taper out into a narrow belt of not over a quarter of a mile in width, which runs along the southern limit of the Archean to beyond Newark.
Another interesting development of the same rocks occurs to the southwest of Red Mills, and thence to the well-known elevations called Iron and Chestnut Hills. The typical hypersthenic gabbro or hyperite of the club-shaped area just described is represented by the so-called "Brandywine granite," which is quarried to such an extensive degree in the neighborhood of Wilmington. It is a rock of dark bluish gray or bluish black color of great hardness and firmness, and is without doubt one of the most valuable and durable stones in existence.**
This rock has been studied in detail by the writer, and from its wide variation in composition and structural characters is of peculiar interest. The rock, as studied under the microscope, is found to consist of a granular mixture of hypersthene, diallage plagioclase feldspar (labradorite), with accessory quartz, biotite hornblende, magnetite, pyrite and apatite.
The most remarkable fact observed in the study of these rocks is the intimate association of highly schistose black hornblende rock with these massive gray gabbros. The black hornblende rock is, after past microscopic studies, found to be but an extreme stage of variation affecting to a greater or less degree the whole gabbro mass. Hornblende, which is the true gabbro is but a rare or accessory constituent, is found to increase in amount until the hypersthene rock passes into a nearly pure hornblende feldspar rock, which from its schistose or banded structure makes it a hornblende gneiss. In the same way it is found that the true gabbros occur in all stages of transition into rocks distinctly granitic in character, or more nearly like many of the European norites or the trap granulites of Saxony.
The massive gabbros, best exposed in the extensive quarries of Brandywine Hundred, are entirely massive in structure, or with an entire absence of those planes of bedding which characterize sedimentary deposits. All evidence obtained in the field and with the microscope confirms the belief that they are truly eruptive, and that the rock was at one time in a more or less molten state, in which condition it was probably forced up through the older mica schists which lie to the north and which also lie buried to the south beneath younger clays of the cretaceous. The banded or schistose structure prevalent in the associated hornblende rocks proves also that the rocks of this gabbro belt have been subjected to great pressure, a pressure which the microscope shows was great enough to flatten and elongate certain of the mineral constituents of the rock and to crush others into fragments.
To the north of the area of gabbros and hornblende rocks, and resting upon the latter, is an extensive formation of highly micaceous slaty rocks, So easily friable as to crumble to the touch, and which break into a loose sandy loam of great richness.
The rocks of the mica schist belt are all stratified with variations of bedding, from that as thin as slate, in the mica schists, to that of a heavily bedded character in more highly metamorphosed forms. Both strike and dip in these rocks are subject to great variation. Variations of strike in this case proving that the elevating force acted very unequally, showing itself in a twisting and undulation of the out-cropping edges of the rock. Variations of dip enabling the geologist, by plotting upon paper those observed along any line of section, to show that the micaceous rocks of Delaware have been pressed into a series of folds or waves, like the wrinkles in a piece of cloth, by an enormous lateral pressure, a pressure which resulted in the elevation of the Blue Ridge from New England to Alabama, of which uplift the crystalline rocks of Delaware form a part.
The mica schists and gneisses of Delaware form a continuation of the so-called Philadelphia Gneiss belt, which covers the greater part of Delaware County, and the southern portion of Montgomery, Bucks and Chester Counties in Pennsylvania.
These rocks have been the subject of much controversy, and their age is still undecided. By many they are regarded as altered Palaezoic sediments, while others continue to regard them as of Archean age. This latter designation is based upon their lithological similarity to many of the older crystalline schists. They have hence been referred to the White Mountain, or the Rocky Mountain series, one of the upper members of the Archean.
Associated with the softer slaty micaceous rocks are probably intrusive masses of coarse grained granite, which vary in thickness for several inches up to many feet. These granites often become so highly feldspathic as to possess considerable economic value, inasmuch as the feldspar frequently becomes decomposed into Kaolin.
The celebrated deposits around Hockessin are of this character. Dixon's quarry near Wilmington has produced very fine yields of feldspar. A very notable vein cuts across the road leading up the Brandywine, about one and a half miles from the head of the State. Its width is about twenty feet, and the material a mixture of red orthoclase albite, blue quartz and muscovite. The rock is quarried for the valuable feldspar, used in the manufacture of artificial teeth.
Quartites are also imbedded with the mica schists and when pure and white are worked under the name of flint. At Tweed's Mill, above Newark, this rock is ground into a fine flour, when it is shipped for use in the manufacture of porcelain ware.
It is an interesting point to note that these quartz veins are frequently of a cellular character, when they are quite similar to many gold bearing veins in rocks of like age in Virginia, North Carolina and Georgia. Hence it is not at all improbable to suppose that gold bearing veins may some day be discovered upon the farms of Northern Delaware.
Another common associate of the mica schists is a black hornblende rock interbedded with the latter, and forming masses often several hundred feet in thickness. In places, this alternation of hornblende and micaceous rocks is frequent.
THE CRETACEOUS. The cretaceous of Delaware, a continuation of the same formation as developed in New Jersey, extends across the state as a northeast and southwest belt, with a breadth of eighteen, and a length of from fifteen to twenty miles. The northern limit of the belt has already been traced out as making the southern boundary of the Archean. The southern limit was a little to the south of, and parallel with, Appoquinimink Creek, cutting through the centre of Noxontown mill-pond, and thence proceeds in a straight southwesternly direction. The different subdivisions of the cretaceous form uniform beds dipping at a low angle to the southeast. This dip was carefully measured at the deep cut, along the Chesapeake and Delaware canal, and found to be at this point at the rate of forty-five feet to the mile.
These subdivisions will be noticed in the chronological table at the opening of this article and will be described in order.
THE PLASTIC CLAYS. This formation is the thickest member of the cretaceous whose northern limit corresponds with the upper border of the cretaceous. Its southern line begins a few miles south of New Castle, and extends in a southwesternly direction to just below Red Lion, crossing the railroad betwen Porter's and Kirkwood, and cutting the State line about two miles north of Chesapeake City.
Although of so much importance, it is, owing to the great thickness of the overlying gravels, rarely exposed, and even when more favorable opportunities are offered, but a few feet of the characteristic Red Clay appear above the surface.
The clay is more generally red and highly plastic; in other cases it is mottled, and again white and sandy like fire clays.
The best exposures are along the lower levels of the gullies cut by the creeks of upper New Castle County, particularly along Red Lion Creek. Occasionally the characteristic red clay comes to the surface at points along the roads. The hills to the east and north of Christiana are formed of these clays, which outcrop very frequently along the road leading from Christiana to New Castle.
Judging from the many points where we have found this clay exposed we are convinced that it has an important economic value for the manufacture of terra cotta ware. The supply is practically inexhaustible, and the clay is to all appearance as good as similar clays worked in New Jersey for manufacture into terra cotta ware.
The plastic clays of Delaware have within the past year been correlated with the so-called Potomac formation of Maryland and Virginia, and have important relations to certain older gravel deposits which will be dwelt upon later.
SAND MARL. This is a deposit of a loamy yellow siliceous sand, with which is mixed some green sand (marl), whose thickness is about ninety feet. It rests upon the plastic clay formation, and covers that part of New Castle County, lying between the southern limit of the plastic clays, and the canal.
THE MARL BEDS. The marl beds cover a comparatively small area in the State, and are practically limited to that division of New Castle county called St. George's Hundred.
The first important outcrops of green sand occur along the Delaware and Chesapeake Canal, the channel of which cuts deeply into the formation. Its northern limit, as determined by old marl pits, runs approximately parallel with the canal, keeping a distance of from a quarter of a mile, to a mile. From this line the marl extends
southward to another boundary parallel with, and about one mile south of Appoquinimink Creek, where it gives place to the tertiary clays.
The divisions of the green sand formation are found, with two exceptions, to correspond with those made by the New Jersey Survey. The chronological table at the opening of this article gives the subdivisions of the marl beds.
LOWER MARL BED. This stratum, which extends as a narrow belt on each side of the canal, is found to outcrop along the entire length of the same, rising about a foot above the surface of the water, and farther west to the height of twenty feet. The lowest layer in this deposit is a tough blueish black marl, which, upon drying, turns to a lighter, ashen or earthy color, when it is found to be made of a mixture of green sand, siliceous sand and argillaceous matter. The solid particles are coated with chalky carbonate of lime, which, under the microscope, appears as a fine white powder of a granular character.
Overlying this last layer is a shelly layer of about three feet in thickness, and containing the characteristic fossils of the Lower Marl Bed of New Jersey.
Above this layer, which we have called the "Black Argillo-micaceous Marl," to the west of the Delaware railroad, it is exposed in the "Deep Cut," where its characters can be well studied. This black marl is composed of minute sharp glassy particles of quartz, coated with a grayish dust, and associated with a few green sand particles of unusual firmness, together with a considerable quantity of minute scales of muscovite mica.
INDURATED MARL BED. The northern limit of this belt, which is also the southern limit of the lower marl bed, starts near the mouth of Scott's run, and thence keeps parallel with the canal to the railroad, where it begins slightly to diverge, cutting the headwaters of the northern branch of the Bohemia river. The southern limit of the belt can only be approximately outlined, but as can best be determined, runs from Port Penn through the headwaters of Drawyer's Creek, and crosses the Maryland line four miles below the head of Bohemia River. The deposit is divided into two layers: 1st, Lower layer of reddish siliceous sand, with some green sand, which occupies the upper border of the belt a little south of the canal; and 2d, An upper layer of partly decomposed or indurated marl, of a rusty green color when dry, which underlies most of the area of the belt.
THE MIDDLE MARL BED. This belt crosses the State with a uniform breadth of three and a half miles, the northern line running from Port Penn, a little north of Drawyer's Creek, and crossing the State line four miles south of the Bohemia River. The southern line crosses the center of the Noxontown mill-pond, keeping parallel with and a little south of Appoquinimink Creek. The middle marl is divided into three very distant layers. (1) A lowermost pure green sand covering most of the belt, and well-exposed along Drawyer's Creek and Silver Run. (2) An intermediate layer of friable shells, from three to ten feet, exposed at the head of Noxontown mill-pond and along the south side of Appoquinimink Creek. (3) An upper yellow or reddish-yellow sand, occupying the southern verge of the belt.
THE ECONOMIC VALUE OF THE MARL. The area covered by the marl beds has already been set forth with sufficient exactness to enable one to know where marl can be found. The supply within the area, underlaid by it, is probably inexhaustible. Its value as a fertilizer makes it worthy of consideration. Green sand is composed of grains of the mineral glauconite, mixed with greater or l'ss quantities of impurities, as clay, siliceous sand, and mineral particles.
Glauconite is a compound of silica, iron, protoxide and potash; the quantity of potash ranging from four to twelve per cent. Many of the New Jersey green sand marls contain from one to two and a half per cent, of phosphoric acid, and there is no reason to doubt but that the Delaware marls, which are geologically identical with those of New Jersey, may be equally rich in this last substance. When used, liberal dressings of the land should be made before plowing, in this way a large amount of potash is introduced into the soil, which, while at first insoluble, or not directly available, becomes slowly set free by decomposition, and renders it available to plants.
The effects of the marl are, therefore, lasting, and when applied every few years permanent. A careful inquiry into the results obtained from the application of marl upon some of the Delaware farms has convinced the writer that good results can be reached by its use. As a direct and immediate source of potash, green sand is not to be compared, by the rule of commercial valuation, with the easily soluble kainit; but as an easily available and cheap material for the culture and permanent improvement of land, green sand marl is a material worthy of the attention of those farmers of the State whose lands are underlaid by it.
THE TERTIARY. All that portion of the State lying south of the lower limit of the marl beds, as already pointed out, is underlaid by the Tertiary, of both Miocene and probable Pliocene age.
The northern half of this area, which is bordered on the south by a line running not far from the course of Murderkill Creek, is underlaid by a drab or white clay deposit of from ten to twenty feet in thickness, so far as can be determined from such well-records as have come to the writer's attention. This deposit contains in places abundant fossils sufficient to determine its Miocene age; it also overlies, probably unconformably, the marl. This highly plastic clay can be seen only along the creeks of Kent County and lower New Castle County.
Along the creeks at Smyrna and at Dover it is frequently exposed, where its qualities can be well studied. In its purer forms it would make an admirable potter's clay, and considering its unlimited supply, underlying as it does the whole of Kent County, its value for that purpose is worthy of the consideration of potters abroad and at home. South of the latitude of Murderkill Creek, representing the whole of Sussex County, we meet with a later deposit of the Tertiary of probably Pliocene age.
This is represented by an uppermost layer of blue clay, and an under deposit of glass sand.
The blue clay varies in thickness from three to ten feet, and often runs into a black bog mud, while less often it becomes of a light drab hue. In its upper portion it contains nests of the modern oyster in a very friable condition, and which Prof. Heilprin, of the Philadelphia Academy of Natural Sciences, considers as of a somewhat antique character.
Underlying the blue clay is the glass sand, which, so far as the writer's knowledge goes, has been penetrated to a depth of forty feet.
It is a pure white glass sand, and would be of great value in manufacturing were it easily accessible. It seldom, if ever, comes to the surface, owing to the overlying clay deposit, which rises to just about tide-level. Where the uppermost gravels and loams of Sussex County are thin, however, it might be found near enough to the surface to be readily worked. At any rate, this point is well worthy of the time necessary for prospecting.
IRON ORE BEDS. The ore beds of the State are found only in New Castle and Sussex Counties, and are entirely bog-ores, which are of two kinds "dome" and "layer." The former is found mostly in New Castle County; the latter in Sussex County.
The outlying spurs of the Archean Rocks, Iron and Chestnut Hills, which rise abruptly above the plain in the vicinity of White Clay Creek in Pencader Hundred, New Castle County, were known to contain ore from the earliest settlement of that part of the State, and the former is mentioned in official records and papers in 1661. In 1725, a forge and furnace were built at the place, where ore was mined and smelted for about ten years. They were then abandoned, and in 1841, the pits and adjacent property were purchased by David Wood, an iron-master of Philadelphia, by whom they were operated for many years, and were known as "Wood's Ore Pits." In 1872, the property passed to the proprietors of the Principio Furnace, by whom they are still owned and operated.
Ore was found on Chestnut Hill, (a knoll about a mile west of Iron Hill,) many years ago. In 1873, the work of mining and shipping ore was begun on quite a large scale, and continued until 1884.
In Sussex County, along the streams that flow westerly into the Chesapeake Bay and largely in Nanticoke Hundred, bog-ores (layer) have been known to exist from about the middle of the last century, and from 1763 to 1776, large quantities of ore were raised, smelted and the iron shipped to England. The blockading of the Chesapeake, compelled the abandonment of the furnaces, and the mining of ore and the manufacture of iron, was not again renewed until the beginning of the present century, when forges and furnaces were built and large quantities of ore raised, some of which was smelted in the forges in the vicinity but the larger portion shipped to New Jersey. The lands from which the later forges procured their ores were those worked before the Revolution. Collins forge, which went out of blast about 1850, was the last to abandon the manufacture of iron in Sussex County. Many of the lands, about 1821, passed to iron masters of New Jersey, who raised and shipped the ore to their furnaces in that State long after the abandonment of all the forges in the lower parts of Delaware. No ore has been raised in Sussex and Kent County for several years, as the visible supply was nearly exhausted; but new deposits are slowly being made, and at some future time the iron industry may again be made a source of profit to the State.
It may be of interest to the people of the region where these ores are found, to know in what other localities similar ores are worked and how they are formed. Professor J.P. Lesley, an eminent authority, in the "Iron Manufacturers Guide," published in 1859, enumerated the different kinds of ore as follows:
"1. The primary, specular, magnetic red oxide, and
2. The brown hematites.
3. The fossil ore of the Upper Silurian Rocks.
4. The carbonates, especially of the coal measures.
5. The bog ores of the present surface."
Professor Lesley continues to speak of the formations and deposits:
"We have the cretaceous, tertiary and post tertiary deposits to the left of the great central belt we go south, covering the southern half of New Jersey, all Delaware and eastern Maryland, eastern Virginia, North and South Carolina, two thirds of Georgia and Alabama, nearly all of Mississippi, the western part of Tennessee and Kentucky between the Mississippi and Tennessee Rivers, and west of the Mississippi River all the country south of Missouri (except a part of Arkansas) as far as the Rio Grande, and northward all between the 99? of longitude and the Rocky Mountains, far into the British possessions, excepting only the Black Hills and a few other and still smaller islands of older rocks which stood above the cretaceous and tertiary oceans, or were projected through its deposits from below. Bog iron ore characterizes this great belt in New Jersey, Delaware and Maryland, and in the west.
"Bog ore is a deposit of every age upon the actual surface at the time. In the present age the process assumes the principal forms the dome and the layer. The former is a mechanical, the latter an organic process. The former takes place at the issues where water sprlngs from ferriferous rocks; the latter at the bottom of peat bogs. Throughout the coal measure areas of the west, where the rocks are outspread for thousands of square leagues in nearly horizontal strata, and their edges exposed upon the sinuous and terraced slopes of innumerable valleys, in alternate bands of slate and sandstone, coal, limestone, iron and clay, the waters, filtering out between these rocks in rows of fountains, deposit the peroxide of iron in those moist places which ferns and mosses most affect, and thus in course of time, domes of wet, spongy, elastic bog arise, composed of an intimate admixture of three elements, the dead and living stems and twigs of vegetation, fine, sandy clay, and the peroxide of iron of the spring water. These domes flatten as their bases expand and sometimes cover a quarter of an acre of the ground, where that is favorable to their reception; for this purpose is required an even, broad and very gently sloping terrace in front of an escarpment of ferruginous sandstone based on clay or coal or on some considerable bed of iron ore. When drained and dried these spongy masses make a favorite fluxing ore for the charcoal furnaces in their neighborhood; but owing to the sulphur they commonly contain make other neutral ores run red-short, and, therefore, should be mixed only with cold short sand ores. By one of these happy adaptations which excite our pleasurable admiration for the laws which govern the material world, these bog deposits fortunately are most common in regions which exhibit heavy silicious ores of cold short temper."
The ores of this nature mentioned above, as the "dome" and formed by a mechanical process, are found mostly in the northwestern part of Delaware in the vicinity of Iron Hill. Professor James C. Booth in his report of 1841 says:
"This elevation consists of clays, sand and gravel, and derives its name from the abundance of boulders of iron-stone and ferruginous quartz scattered over its flanks, the latter of which was probably at one time of good quality, but through exposure to atmospheric agents, has been rendered valueless. An excavation has been made on the summit for the extraction of iron ore to the depth of 40 to 50 feet, which enables us to estimate the character of this singular hill. . . .
"Nodules of iron ore are abundantly distributed through the whole formation; it is of a chestnut-brown color (sometimes blueish-black from the presence of manganese), hard and tough; may be considered a moderately hard ore, being both siliceous and argillaceous; the nodules frequently enclose an ochrey clay, more rarely a black earth containing manganese. Large quantities of the ore have already been exported."
Professor Lesley continues in regard to layer ore:
"But ore of another kind is deposited upon the white clay or white sand floor of peat bogs, lakes and swamps of every kind in tertiary, and other low and gravelly parts of the earth's surface. In Eastern Massachusetts the oldest furnaces were built to smelt such ores. In New Jersey and Delaware they have been wrought many years. The southern shore of Lake Erie is lined with furnaces built on deposits of this order. In true peat bogs a cake or pan of peroxide of iron is found at the bottom, and every tree-trunk is dyed black with it. The waters which feed these bogs bring into them from the ferruginous sand hills, by which they are inlocked, enough of iron to supply certain microscopic animals with the material they require for their ferro-siliceous shields, and these, upon the death of the little creatures, fall in a fine powder to the bottom of the bog or are carried into the pores of the timber it contains."***
The ores of this State are not, however, those formed in peat swamps but are better described by Professor James C. Booth in his report in 1841. Under the head of "Upper Sands," he writes:
"The ores of iron found in various parts of Sussex County in considerable quantity, and particularly on the dividing ridge, claim attention as having yielded and still introducing some revenue into the State. The most remarkable are those situated a few miles northwest of Georgetown, near the sources of several streams flowing westerly, which, being on elevated and level land, spread themselves in broad and shallow basins covered with a stratum of black argillaceous mould. The ore found below this black soil is of various kinds, hard or solid, gravelly and loam ore. The hard variety, which exists in great abundance, forms a solid substratum to the mould from six to eight inches or more in thickness; it is hard, moderately tough, of a rich brown color and resinous lustre, with an uneven, conchoidal fracture; sometimes compact; often cellular in structure; composed essentially of peroxide of iron and water. An analysis of this variety of ore from the Clowes bed (in the western part of Broadkiln Hundred), performed by E. Mayer, yielded peroxide of iron, 80 per cent.; water, l5 per cent.; silica, 5 per cent., and of alumina a trace, which may be viewed as the average composition of the same kind found in other localities. The amount of metallic iron in the above is 55 1/2 per cent., but when subjected to roasting the remaining ore will yield nearly 66 per cent. The gravelly ore consists of irregular masses of a similar ore of the size of a nut and smaller, disseminated in a yellow ferruginous loam, but containing rather more argillaceous matter, is softer and more readily worked.
"The loam ore, which is still softer than the preceding, is a yellow ochre or clay highly charged with hydrated peroxide of iron. For working in the furnace the several kinds are mingled together, which not only facilitates the reduction by fluxing, but results in the production of a better quality of iron. Various names have been given to the ores of Sussex, more dependent on differences in their external form and other characters of the ore, which first renders itself perceptible in the metal; it is that matter which forms a cold, short metal, and, in all probability, is a compound of phosphorus or arsenic, but analysis has not hitherto detected their presence in the ore. The hard or solid variety is very apt to produce such a metal, but by mixing with the softer kinds, the result is a good malleable iron when worked in a forge.
"Collins ore bed, the lowest on the Green Meadow branch of Deep Creek (in Nanticoke Hundred), consists chiefly of a solid loam ore which is principally wrought at Collins forge a hard, compact ore, very rich in iron, but said to yield a cold, short metal, and of a small quantity of sandy ore. There are many other deposits of ore in various parts of Sussex, such as that on Green branch, about ten miles west of Millsborough, the best of which is in balls or nodules and yields good metal; that on Burton's branch, one mile west of the same town, making a cold, short iron; that on Little Creek, near Laurel, and others in which the characters are referable to those given above. . . .
"The raising of ore in quantity was commenced about 1814, since which time nearly 200,000 tons have been raised, about 190,000 of which were exported, introducing not less than $600,000 into the State."
At the time Mr. Booth made his report little was known concerning the manufacture of iron before the Revolution and mining of the bog ores. A full account of the mining of ore and manufacture of iron will be found in histories of the hundreds in which the furnaces and forges were located.
THE QUATERNARY. Overlying all of the formations of the State, and forming its soil, is a broad sheet of gravelly deposits, whose average thickness is about twenty-five feet. In New Castle County these gravels have received the name of Delaware gravels, from their identity with like deposits along the Delaware River valley. Here we distinguish two layers; an upper brick clay, called the Philadelphia brick clay, and an under red sand and gravel. The brick clay layer has a thickness varying from two to six feet, but with an average of about three feet. It varies from a stiff brick clay to a loam of remarkable richness, which forms the soil of New Castle County. It often becomes quite gravelly, containing frequently quartzose boulders and cobble stones of huge size. The red sand has an average thickness of about twenty feet, and is characterized by its color. The sand is often quite fine, again coarse and running into gravel; it shows frequent cross-bedding, and indicates the agency of swift, shifting currents in its deposition. The Delaware gravels extend up the slopes of the Archean hills to an average elevation of two hundred feet, which represents the height of the waters of Quaternary time.
Over Kent County the gravels maintain an equal thickness; the brick-clay layer, however, becomes more sandy, and more generally a sandy loam, this deposit forming the rich peach land of Kent County.
In Southern Kent County the two members of the Quaternary gravels merge into a single deposit of a highly gravelly or loamy character, this feature continuing over the whole Sussex County.
To explain the mode of deposition of these gravels, we must understand that during the Glacial epoch, what is now the Delaware River had its source near Belvidere, at the lower limit of the ice sheet; that it stood one hundred and fifty feet higher than at present, and had a width of something like ten miles.
At the same time, what is now the Delaware and Maryland Peninsula, became submerged, forming an estuary like the Chesapeake; into this the swollen Delaware River emptied, carrying with it its loads of detritus, which it spread out over the Peninsula.
Down this Quaternary river icebergs floated carrying burdens of boulders, which they dropped at points over the entire State.
Besides this universal sheet of gravel covering all three counties, we find over the high Archean hills isolated patches of gravel, which are much older. This is called the Potomac formation by W.T. McGee, from its fine exposures along the Potomac River. McGee as shown that these isolated patches of gravel are contemporaneous with the plastic clays of the Lower Cretaceous, when the clays extended farther north, so as to reach over the high hills of Delaware.
The materials of the Potomac gravels are quite like those of the Delaware gravels, but the two can easily be distinguished, from the fact that the Potomac gravel patches reach an elevation of from three hundred to four hundred feet, while the Delaware gravels never reach that elevation, but have a maximum elevation of two hundred and twenty feet above tide.
* Contributed by Prof. Frederick D. Chester, of Delaware College.
** Bulletin, No. 41, U.S. Geological Survey, Washington.
*** "Ehrenberg has detected in the ochreous matters that form bog iron ore immense numbers of organic bodies which indeed make up the substance of the ochre. They consist of slender articulated plates or threads partly siliceous and partly ferruginous, of what he considered an animalacule, but which are now commonly regarded by naturalists as belonging to the vegetable kingdom." Appleton's Cyclopedia.
SOURCE: Page(s) 4 - 8, History of Delaware, 1609-1888, Volume One by Scharf, Thomas J., Philadelphia; L.J. Richards & Co., 1888