54 
PALAEONTOLOGY OF NEW-YORK. 
formations in New-York, and their relations to the geology of other 
parts of the United States, this series must form a very prominent 
feature; nor can we have a clear view of the Palaeozoic series, so well 
displayed in most of its members in New-York, without embracing in 
our consideration the formations so conspicuous in the exhibition of 
the ancient subcarboniferous faunae. 
In the Mississippi valley, at several points in Illinois, Iowa and 
Missouri, the strata of the Chemung group are succeeded by calcareous 
beds of gray, reddish brown, or ferruginous subcrystalline limestones. 
Although the line of demarcation is not strongly defined, both the rock 
and the fauna soon show a strong contrast to that of the group below. 
The crystalline limestone is a crinoidal limestone par excellence. Some 
portions of the rocks are composed almost wholly of the broken and 
comminuted remains of this family of fossils; so that, after a little 
weathering, the mass is scarcely coherent. The higher portions are 
usually more compact, lighter colored, and often a white semicrystalline 
limestone. 
This formation is more or less fossiliferous throughout, and while 
remains of Crinoidea are by far the most abundant and important forms, 
several species of Brachiopoda are very conspicuous. From the readily 
determined sequence, and the fine exposure of the rock which has 
afforded so many beautiful fossils at Burlington, Iowa, that name has 
been proposed to designate this formation. 
Next above the Burlington limestone are thick and extensive cherty 
layers, forming beds of passage to the succeeding formation, the Keokuk 
limestone, which is well seen at Keokuk, Iowa, and on the opposite side 
of the Mississippi river in Illinois. This occurs as heavy-bedded bluish 
or grayish blue subcrystalline limestone with shaly partings, and 
sometimes with thicker strata of shale and shaly limestone. The same 
rock occurs in Missouri in numerous localities, always distinct, and 
recognized by its lithological character and by its fossils. This import¬ 
ant formation marks the second stage or epoch in the accumulation of 
the great limestone series of this period. 
