«• PAL5:0NT0L0GY 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 



