  The properties of old globular cluster systems (GCSs) in galaxy halos offer
unique insight into the physical processes that conspire to form any generic
star cluster, at any epoch. Presented here is a summary of the information
obtained from (1) the specific frequencies (total populations) and spatial
structures (density vs. galactocentric radius) of GCSs in early-type galaxies,
as they relate to the efficiency (or probability) of bound cluster formation,
and (2) the fundamental role of a scaling between cluster mass and energy among
Galactic globulars in setting their other structural correlations, and the
possible implications for star formation efficiency as a function of mass in
gaseous protoclusters.
