282 



/. CULVER HARTZELL 



Fig. 13. — Cast of the exterior. 



quantities of corals, bryozoans, and crinoids. The brachiopods 



are more or less preserved as originals. The sponges, gastropods, 



annelids, and crustaceans are well represented. The lamellibranchs 



and cephalopods, however, are absent. 



The Paleozoic hexactinellids occur in groups of strata containing 



other organisms; but in their 

 own particular beds the 

 absence of other forms is 

 striking. In Steuben county, 

 N. Y., the formation is a 

 sandstone which is fine-grained 

 and argillaceous, and contains 

 very few crinoids and brachio- 

 pods; but Hydnoceras tube- 

 rosum occurs in abundance.^ 

 The fossils in the sandy 

 and gravelly deposits of the 



Potsdam, the Medina, the Chemung, the Catskill, the coarse con- 

 glomerates of the Lower Carboniferous, or the calcareous grit of 



the Schoharie and Oriskany, all show different conditions of 



preservation. 



The trilobites in the 



Potsdam of Wisconsin and 



Minnesota are badly broken 



up. In the Cambrian of 



Wisconsin we find argillaceous 



layers in which are molds and 



casts. The Medina sandstone 



contains poorly preserved 



fossils, and shows molds of ^ 



the interior. 



In the calcareous sandstones 



of the Chemung we find well-preserved organisms ; but in the Catskill 



sandstones they are poorly preserved. 



The Utica, Marcellus, and Genessee slates show well-preserved 



originals; but the majority of the fossils are molds. 



I Beecher, Memoirs of the Peabody Museum, Yale University, Vol. II, Part i. . 



Fig. 14. — Cast of the interior. 



