96 



CARBONIFEROUS LIMESTONES OF 10 W A. 



Superimposed upon this oolitic bed are more than a hundred feet of crinoidal 

 limestones, containing a great variety of beautiful species, belonging chiefly to the 

 genera Pentremites, Platycrinus, CyatJwcrinus, Actinocrinus, and Poteriocrinus, many 

 of which are figured on Table V., A and B. 



For variety and elegance of form, the species afforded by the Burlington beds of 

 this subdivision, are probably unrivalled. In the Hannibal beds, they are neither 

 so perfect nor so numerous. Interposed between the crinoidal beds of these two 

 localities, are white, semicrj-stalline, and semioolitic beds, in which the genera 

 Productus and Spirifer are, also, abundant. 



Above these encrinital beds occur the shell-beds, so designated, because especially 

 rich in remains of Brachiopoda, particularly of the genera Productus and Spirifer. 

 These beds afford, however, a considerable variety of other fossils, Capulus, 

 Cardivm, Phittipsia, and the teeth of certain fishes, belonging to the genus 

 Psammodas, the remains of which contrast beautifully, in their rich, brown 

 colour, with the cold, light-gray of the embedding limestone. 



The thin-bedded limestones, which, in the ascending order, succeed these, contain 

 a considerable variety, both of Bracliiopods and Encrinites ; but their distinguishing 

 characteristic is the presence of those screw-shaped, reticulated corals, known as 

 Archimedes (Table IV., Fig. 1). This fossil has, in these beds, a vertical range of 

 about fifty feet, reaching to the top of the lower series. 



The geodiferous group, at the base of the upper series, contains few, if any, 

 organic remains. In the magnesian beds above are found lamelliferous, reticulated 

 corals, referable to the genera Fenestella, Gorgonia, Retepora, and Cellepora. Also 

 a Chcetetis, Terebratula Jamellosa, and a few other fossils. 



In the gritstones comprising the third group, no fossils have been detected. 



The fourth group, or Lower Concretionary Limestone, is chiefly characterized by 

 a species of Lithostrotion, described by Lesueur under the name of Stylina* from 

 the styloid process which forms the axis of its terminating cells, and usually 

 projects conspicuously above their general surface ; especially when the fossil is of 

 a cherty nature, as it usually is when occurring in this geological position. 



This fossil coral, it would seem, is as abundant in Iowa as is the LitJiodendron 

 (Diphyphyllum of Lons.) in the vicinity of Kettlewell; and occupies the same 

 geological position. It is also worthy of remark, that though these two corals 

 have been referred to distinct genera, both have a prominent central axis, and 

 otherwise so closely approximate to each other in external structure, that they are 

 not easily distinguishable apart. 



The white and brown gritstones of the fifth group occasionally contain impres- 

 sions of Catamites, Lepidodendrons, and other plants of the coal-measures. 



The sixth and uppermost group of the carboniferous limestone is, for the most 

 part, destitute of fossils. Locally, a few small Terebratulge and Spirifers have been 

 noticed. 



* Table IV., Figs. 5 and 6. 



