20 New York State Museum 



mass to the east. Several of these reefs have been 

 definitely located ; one extending through eastern New 

 York and Pennsylvania, a second in western New 

 York, a third passing through northern Ohio and a 

 fourth through northern and western Michigan. Tube 

 corals and hydrocorallines (Stromatopora) are abund- 

 ant in these reefs but the forms chiefly found are the 

 honeycomb corals (Favosites) and star corals (Cras- 

 pcdophyllum etc.) Bryozoans secrete structures of 

 carbonate of lime and recent forms are found incrust- 

 ing seaweeds, rocks etc. Fossil bryozoans formed 

 branching, often cylindrical, masses or grew in sheet- 

 like associations which formed the basis of limestone 

 beds. Bryozoans, like corals, have formed reefs. 

 Brachiopods and mollusks are the important shell- 

 bearing animals. Shells of brachiopods, pelecypods 

 and gastropods have formed beds of limestone in the 

 geologic past. The shells of pteropods form a deep- 

 sea pteropod ooze today and in the older geologic ser- 

 ies the shells of such animals entirely make up lime- 

 stones, as the Upper Devonian Genundewa lime- 

 stone ("Styliolina limestone") of western New York. 

 This limestone contains immense numbers of the 

 minute pteropod Styliolina fissurella. Cephalopods, 

 such as the Ammonites of the Mesozoic, have been 

 so abundant as to build up beds of limestone. In cer- 

 tain New York formations, as the Watertown lime- 

 stone of the Black River beds (Ordovician) and the 

 Cherry Valley (Agoniatite) limestone of the Marcellus 

 shale (Devonian), the cephalopods are in places very 

 abundant. Crinoids together with blastoids and 

 cystoids have been important as rock-formers during 

 Paleozoic and Mesozoic times, forming what are 



