<p>Regarding your question:</p>

<blockquote>
  <p>So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.</p>
</blockquote>

<p>The short answer is no. The layer seems to be about 1 meter thick. No bombardment related fire can cause blackening 1 meter deep.</p>

<p>Now, why is it "black"? First of all, it's not black. It's dark brown. I've seen black soils, and trust me - they are pitch black. There are several reasons for it. My best guess is that it's simply moist. You know how things appear darker when wet? Same here. My hint is the floor of the site. I'm guessing it's the same material, but it's drier so it looks lighter.</p>

<p>There are more reasons, some concerning the organic content of the soil (for example, peat - a highly organic black soil) or the mineral content of the soil (soil composed of high iron contents will also appear black).</p>

CC BY-SA 3.0
2014-09-12T00:00:57.750Z
I agree that on the picture it looks more like a darker brownish layer. My camera does not seem to be working that well. In real life it is even darker, to the point of being black. However, what you're saying about the thickness of the layer makes sense and I thought about it too. The city was burning for days with bombardment being stretched over a period of days also, so I thought the already disturbed earth might make it easier for explosive material to enter deeper grounds, hence the thickness. Anyway, if your expert opinion is that it is not so, I'm fine with it also :D
Spraygun
CC BY-SA 3.0
2014-09-16T00:38:24.860Z
Michael, In my area, the soil contains lots of iron. Rather than being darker, it is red, from oxidization. Humus shouldn't be found in a layer like that, unless some excavator in the past had been clumsy enough to bury the topsoil. In my area, some areas of subsoil varies from the regular red or orange, and are darker, like what is pictured above. I think it's mostly shale, in those areas.
J. Musser
CC BY-SA 3.0
2014-09-16T03:49:46.813Z
I meant iron as in iron bearing minerals, mostly shales. Not proper "iron minerals" such as hematite and various iron oxy-hydroxides.
Gimelist
CC BY-SA 3.0
2014-09-17T00:45:27.720Z
After it was raining all day yesterday the "blackness" of the layer was a lot clearer to see. Directly underneath the rubble and quite distinct from the darker brown underneath it. Unfortunately I didn't have my camera operational, but I'm hoping tomorrow it's still as visible as today and that I get a better shot of it.
Spraygun
CC BY-SA 3.0
2014-09-17T05:06:51.307Z
How thick is the black layer and is this thickness constant throughout the site?
Gimelist
CC BY-SA 3.0
2014-09-10T17:33:56.840Z
2014-09-10T17:33:56.840Z
Gimelist
<p>I have this construction site right outside my house, which I would like to give you some geographical background about before asking my question. Have a picture first though </p>

<p><img src="https://i.sstatic.net/fs1sc.jpg" alt="Construction Site">
<br/></p>

<p>There used to be industrial buildings of red clay bricks like the piece of wall still remaining. These walls, however, had a white stone facade around them so I'm not too sure the wall still standing was indeed part of the structure before demolition.</p>

<p>The city I live in is Dresden, Germany and the district I live in was a major bomb dropping zone during WWII. For some reason in my district they decided to just let some walls of otherwise vanished old structures be and use them to mark estate borders, or to just be there really, which looks quite beautiful in some cases.</p>

<p>Seeing this construction site I cannot help but notice this black layer of earth under what seems to be a layer of rubble. Even though its not that noticeable on the left side, its continuous throughout the hole and starts appearing at the same height. </p>

<p>As I said before, this area used to be exposed to heavy bombardment. So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.</p>

<p>Or is it, perhaps, a natural occurrence in slightly deeper depths, for the soil to turn that dark?</p>

CC BY-SA 3.0
2014-09-09T00:47:11.273Z
A really good way to answer this question, which probably needs a site inspection to be sure, would be to do a soil decomposition test. Get a large jar, and crush up some soil as fine as you can (might help to dry it out first), then fill the jar about 1/3 full of soil, and then fill almost to the top with clean water. Now shake the bejeesus out of it, until it's mixed really well. Then sit it down somewhere, and wait for it to settle. Once it's settled, you'll be able to get a basic estimate of the composition - gravel at the bottom, clay at the top, and hummus below the clay or floating.
naught101
CC BY-SA 3.0
2014-09-09T00:49:48.957Z
A close up image of that bank would be useful, too.
naught101
CC BY-SA 3.0
2014-09-09T18:15:03.280Z
Being a professional landscaper, my instinct would be to do like I always do, and send a sample to a lab for analysis. I do it to fnd the pH and nutrient levels, and organic matter content, but you *could* get a complete analysis of all the composites of that particular sample.
J. Musser
CC BY-SA 3.0
2014-09-11T23:52:25.553Z
Hi thanks for the suggestions. Unfortunately I have no way to access the construction site, so getting samples is not really an option.
Spraygun
CC BY-SA 3.0
2014-09-16T00:39:32.757Z
@Spraygun Why can't you walk in? I'm assuming that equipment didn't spawn in there. Or maybe, you'd have to ask first.
J. Musser
CC BY-SA 3.0
2014-09-17T00:41:11.580Z
I sure hope this isn't a heavy duty machine mating ground! They sealed the site off to all sides with multiple fences and locks to cross. Unfortunately for the past few days construction has been going on from dusk till dawn so in daylight there is no sneaking in. I could indeed, however, walk by the office and just ask someone there, maybe this person has an answer to my original question also. Being more familiar with the grounds here.
Spraygun
<soil>
Why is a layer of the subsoil so dark on this construction site?
Spraygun
# Why is a layer of the subsoil so dark on this construction site?

(Asked by: username_0 on 2014-09-06)

I have this construction site right outside my house, which I would like to give you some geographical background about before asking my question. Have a picture first though

![Construction Site](https://i.sstatic.net/fs1sc.jpg)

There used to be industrial buildings of red clay bricks like the piece of wall still remaining. These walls, however, had a white stone facade around them so I'm not too sure the wall still standing was indeed part of the structure before demolition.

The city I live in is Dresden, Germany and the district I live in was a major bomb dropping zone during WWII. For some reason in my district they decided to just let some walls of otherwise vanished old structures be and use them to mark estate borders, or to just be there really, which looks quite beautiful in some cases.

Seeing this construction site I cannot help but notice this black layer of earth under what seems to be a layer of rubble. Even though its not that noticeable on the left side, its continuous throughout the hole and starts appearing at the same height.

As I said before, this area used to be exposed to heavy bombardment. So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.

Or is it, perhaps, a natural occurrence in slightly deeper depths, for the soil to turn that dark?

**Tags:** soil

> **Comments:**
> **username_1**: A really good way to answer this question, which probably needs a site inspection to be sure, would be to do a soil decomposition test. Get a large jar, and crush up some soil as fine as you can (might help to dry it out first), then fill the jar about 1/3 full of soil, and then fill almost to the top with clean water. Now shake the bejeesus out of it, until it's mixed really well. Then sit it down somewhere, and wait for it to settle. Once it's settled, you'll be able to get a basic estimate of the composition - gravel at the bottom, clay at the top, and hummus below the clay or floating.  
> **username_1**: A close up image of that bank would be useful, too.  
> **username_2**: Being a professional landscaper, my instinct would be to do like I always do, and send a sample to a lab for analysis. I do it to fnd the pH and nutrient levels, and organic matter content, but you *could* get a complete analysis of all the composites of that particular sample.  
> **username_0**: Hi thanks for the suggestions. Unfortunately I have no way to access the construction site, so getting samples is not really an option.  
> **username_2**: @username_0 Why can't you walk in? I'm assuming that equipment didn't spawn in there. Or maybe, you'd have to ask first.  
> **username_0**: I sure hope this isn't a heavy duty machine mating ground! They sealed the site off to all sides with multiple fences and locks to cross. Unfortunately for the past few days construction has been going on from dusk till dawn so in daylight there is no sneaking in. I could indeed, however, walk by the office and just ask someone there, maybe this person has an answer to my original question also. Being more familiar with the grounds here.  

---

## 1 answers

### Answer by username_3 on 2014-09-10. Score: 5 | Accepted answer

Regarding your question:

> So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.

The short answer is no. The layer seems to be about 1 meter thick. No bombardment related fire can cause blackening 1 meter deep.

Now, why is it "black"? First of all, it's not black. It's dark brown. I've seen black soils, and trust me - they are pitch black. There are several reasons for it. My best guess is that it's simply moist. You know how things appear darker when wet? Same here. My hint is the floor of the site. I'm guessing it's the same material, but it's drier so it looks lighter.

There are more reasons, some concerning the organic content of the soil (for example, peat - a highly organic black soil) or the mineral content of the soil (soil composed of high iron contents will also appear black).

> **Comments:**
> **username_0**: I agree that on the picture it looks more like a darker brownish layer. My camera does not seem to be working that well. In real life it is even darker, to the point of being black. However, what you're saying about the thickness of the layer makes sense and I thought about it too. The city was burning for days with bombardment being stretched over a period of days also, so I thought the already disturbed earth might make it easier for explosive material to enter deeper grounds, hence the thickness. Anyway, if your expert opinion is that it is not so, I'm fine with it also :D  
> **username_2**: Michael, In my area, the soil contains lots of iron. Rather than being darker, it is red, from oxidization. Humus shouldn't be found in a layer like that, unless some excavator in the past had been clumsy enough to bury the topsoil. In my area, some areas of subsoil varies from the regular red or orange, and are darker, like what is pictured above. I think it's mostly shale, in those areas.  
> **username_3**: I meant iron as in iron bearing minerals, mostly shales. Not proper "iron minerals" such as hematite and various iron oxy-hydroxides.  
> **username_0**: After it was raining all day yesterday the "blackness" of the layer was a lot clearer to see. Directly underneath the rubble and quite distinct from the darker brown underneath it. Unfortunately I didn't have my camera operational, but I'm hoping tomorrow it's still as visible as today and that I get a better shot of it.  
> **username_3**: How thick is the black layer and is this thickness constant throughout the site?  

---

