96 
PALAEONTOLOGY OF NEW-YORK. 
The Ferruginous sandstone is succeeded by a limestone formation, 
having lithological affinities with the lower limestone, but very dis¬ 
tinctive in its organic remains. The Kaskaskia limestone is a well 
marked group, consisting of gray or ferruginous subcrystalline beds of 
dark-colored limestone, with shaly partings, and sometimes with thick 
seams and beds of shale; with intercalated beds of sandstone, and of 
shale, sometimes with land plants. The fauna is everywhere distinctive, 
though consisting mainly of genera known in the lower limestones, and 
marked also by the presence of Archimedes. The crinoidean fauna, so 
characteristic of the Carboniferous limestone series, has few species of 
the actinocrinoid type, and fewer Platycrinus than the Burlington and 
Keokuk limestones; while Poteriocrinus is much more fully developed, 
'and the species of Zeacrinus and Scaphiocrinus become the most nume¬ 
rous and important forms. 
The Kaskaskia limestone is the uppermost member of what I have 
termed the Carboniferous limestone formation of the Mississippi valley. 
To it succeeds the Coal measures in the true order of sequence; though, 
as we shall find, the series is interrupted, and the rocks of that 
period do not always rest on this group of limestones. 
In considering the geographical distribution of the groups of strata, 
there are many interesting facts in connection with the conditions 
attending the accumulation and deposition of these limestones. 
The lowest or Burlington limestone has the greatest northerly exten¬ 
sion, and the northern outcrop of the Kaskaskia limestone, so far as 
we know, never approaches within one or two hundred miles of it; and 
we have also satisfactory proof that this absence of the upper limestone 
is not due to denudation, but that these were the limits of original 
accumulation on the north. 
In tracing these several formations to the southward, we find that 
the Burlington limestone has its most perfect development north of the 
parallel of the Ohio river. In Tennessee and Alabama the place of this 
formation is represented by the cherty beds, constituting a part of what 
is there known as the “ Siliceous group,” and a very partial exhibition 
