320 New York State Museum 



on the surface after weathering of the underlying Medina 

 sandstones. To these shales and sandstones below the 

 Thorold have also been given the names Grimsby sand- 

 stone from Grimsby, Ontario, and the Cataract formation 

 (Schuchert '14), named from its occurrence at the cata- 

 ract of the Credit river, Ontario. The Grimsby and 

 Cataract are largely equivalent and interfingering local 

 phases of the Upper Medina and not strictly separable 

 time divisions of the group. The Whirlpool sandstone is 

 the clastic base of the Cataract. At, or rather just above, 

 the top of the typical Upper Medina shales (Grimsby) 

 in the Thorold sandstone is found the worm trail Arthro- 

 phycus alleghaniensis (harlani), a very characteristic and 

 widely distributed fossil that marks the beginning of the 

 Clinton group. The brachiopod Lingula cuneata is a 

 characteristic Upper Medinan fossil, occurring in abun- 

 dance in certain beds in the light-colored sandstone. There 

 is a sparse fauna in the Albion sandstone, but while a 

 large part of this formation is barren, a fair fauna has 

 been found in the quartzose beds and in part listed (Ul- 

 rich '26). No fossils have been found in the lower beds 

 of these Upper Medina sandstones; in the upper 25 or 

 30 feet a small fauna has been found including bryozoans, 

 brachiopods (IV hit field ellas as W. oblata etc.) and gas- 

 tropods (Bucanella trilobata, Pleurotomaria (Euconia?) 

 pcrvetusta etc.) 



From the middle or typical part of the Upper Medina 

 sandstone at Lockport has come a considerable fauna (44 

 listed; Ulrich '26) of bryozoans (Phaenopora explanata, 

 Lioclemella cf ohioensis, Hclopora cf fragilis etc.), 

 brachiopods (Lingula cuneata, W hit field ella oblata, 

 Rhynchotrema plicata etc.), pelecypods (Ctenodonta, 

 Modiolopsis, Cleidophorus, Ischyrodonta, Orthodesma, 



