2.32 
The American Geologist. 
April, 1904. 
and the most important from the water are zoogenic (organic 
limestones). 
DiAGKAM I. — Interrelations of thh Endoghnktic Rocks. 
The material of the earth may be in three states before solidification, i. e.,- 
that of fusion, of solution in water, and that of vapor. From these states by 
direct deposition (endogenetically) we get the three types of fundamental 
rocks, the Igneous or Pyrogenic, the Aqueous or Hydrogenic, and the Atmosp- 
heric or A tmo^en/c. (Snow and snow-ice). By the physiological activities of 
organisms, we have formed the Organic or Biogenic rocks, the material of 
which is either derived from the Atmosphere (chiefly through plants — Pbyto- 
geaic, though also in a minor degree through animals, as indicated by the 
heavy dotted line) or from the water (chiefly through animals — Zoogenic, 
though also in a minor degree through plants). The lighter arrows show to 
which states the rocks finally return, the dotted lines indicating the less likely 
change. Biogenic rocks are either vaporized or dissolved, hence the return 
arrows arise from the center. Pyro-atmogenic rocks, half way bet\veen Pyro 
and Atmogenic, are illustrated by sublimates, and Pyro-hvdrogenic rocks, half 
way between Pyro and hydrogenic, by pegmatites. 
We may omit further discussion of the pyrogenic or igneous 
rocks, as they have been made the special study of many in- 
vestigators. The atmospheric rocks may likewise be dismissed> 
since the only important member of this group is snow, and its 
consolidation product,* snow-ice. The hydrogenic and bio- 
genic rocks, on the other hand, tooether with the class of clastic 
Through diagenic metamorphism or diagenesis. See belcw. 
