04 PALEONTOLOGY OF NEW-YOKK. 



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. 



