Handbook of Paleontology 323 



cods has brought out the fact that they occur in more or 

 less clearly distinguishable zones. Nine of these zones 

 have been recognized (Ibid; 349-91), three for each of 

 the major divisions of the Clinton (Lower Clinton: 1 

 Zygobolba erecta, 2 Z. antic ostiensis, 3 Z. decora; Middle 

 Clinton : 4 Z. eniaciata, 5 Mastigobolbina lata, 6 Zygosella 

 postica; Upper Clinton: 7 Bonnemaia rudis, 8 Mastigo- 

 bolbina typus, 9 Drepanellina clarki zones). These fossil 

 zones serve mainly in giving an approximate indication 

 of particular horizons in an otherwise very uncertain se- 

 quence of deposits. Favorable exposures, that is, per- 

 fectly exhibited sections, are seldom found and the suc- 

 cessive beds of shale and sandstone are much alike in 

 lithologic character and many are practically barren of 

 organic remains. 



The character and relations of the Clinton divisions in 

 New York may be pretty well understood from a study 

 of the sections exposed in the gorge of the Genesee at 

 Rochester (figure 46) and at Clinton, the type locality. 

 The Middle Clinton with its wealth of very characteristic 

 ostracods, which occurs at the type locality, is not found 

 in the Rochester section and, indeed, is restricted to east 

 of Lakeport. 



In western New York the Lower Clinton begins with 

 the Thorold sandstone ("Gray Band"). This is a hard, 

 gray sandstone, five to 12 feet thick, named from its 

 occurrence at Thorold, Ontario (Grabau '13). A few 

 fossils are present in this sandstone, among them bryo- 

 zoans and the brachiopod Rhipidomella. At Niagara 

 Falls this band rests on mostly red sandstones of the 

 Upper Medina, representing the closing marine stage ; be- 

 tween Lockport and Rochester it rests upon various older 

 sandstones of the Upper Medina; and going eastward 



