THE CARBONIFEROUS SYSTEM. 103 
In Illinois the Lower Carboniferous formation is, for the most part, cal- 
careous. It consists of— 
1. The Chester or Kaskaskia limestone. 
Der Mel Sts MeOUISMITMEStONCla css ciscccsceceseus cctecaseslesetenen es 250 feet thick. 
oo ee bivenWarsaw? LIMEeStONes 2.0... cccsce cscs ee ces Sete eee Uy cee 50 to 100 ¢ 
Aree WiC ACEO UKM ESTON CI +. Se teces seelecccccess Sescescte suceesitee 40 to 50 § 
Dennis mala etomylineStOMeb cs ccceclerscccotcecs orosssleceescsss 60 to 100 ch 
All of which are underlaid by the “‘ Kinderhook group,” consisting of 
shales and sandstones, with some local limestone beds having a thickness 
of about 100 feet. The Illinois series contains many fossils which are 
identical with those found in the Waverly of Ohio, and we have every 
reason to believe that the beds which include them are the equivalents 
of each other ; the lithological differences which they present being due 
to the fact that the Waverly of Ohio is a shore deposit, while most of the 
Lower Carboniferous of Illinois was laid down in an open sea. The reach 
of this sea is indicated by the spread of its calcareous sediments; and 
since the Coal Measures of Michigan, Illinois, Kentucky, Tennessee, 
Alabama, and Virginia are underlaid by this calcareous stratum, we have 
in this evidence of a continuous ocean, which, during a portion of the 
Lower Carboniferous period, occupied the area of the States that have 
been enumerated, but which reached no farther (at least in sufficient 
purity to form limestones) than central Ohio and the southern line of 
Pennsylvania. 
It is also evident that the Lower Carboniferous period was one of pro- 
gressive continental depression, for the lower rocks deposited in this period 
over a great area are mechanical sediments, while the overlying calca- 
reous deposits, thickest at the south and west, gradually thinning out 
toward the north and east, are by their volume a measure of the length 
of time during which, in any locality, marine conditions prevailed. 
Hence we must suppose that the thin edge of the calcareous member of 
the Lower Carboniferous series represents the uppermost, last formed 
portion of the mass; and this is more widely extended than the lower 
beds, because, at the time of its deposition, the sea had further encroached 
upon the land. 
THE CARBONIFEROUS CONGLOMERATE. 
In many parts of Europe, especially in England, and throughout most 
of the area occupied by Carboniferous rocks in America, the middle por- 
tion of the Carboniferous series is indicated by a mass of sandstone, of 
greater or less thickness, containing vast numbers of quartz pebbles, and 
forming a pudding-stone, or conglomerate. In England this rock is 
