EXTENT OF FOLDING AND SUBSEQUENT EROSION 461 



and Oswego. Beyond this point it is represented by the Oneida con- 

 glomerate, and both formations are to be regarded as the overlapping 

 upper portions of the Tuscarora quartzite of Pennsylvania. In western 

 New York and Canada the Thorold quartzite is seldom over 10 or 12 feet 

 in thickness, but on the extreme northwestern point of its occurrence, in 

 the township of Nottawassaga, Ontario, it is said to be 35 feet thick. 

 This is about 350 miles in a direct line from the outcrops in central Penn- 

 sylvania. Where the Keppel dolomites are absent, as in the region south- 

 east of Collingwood generally, the line of division between the Queenston 

 and Medina beds becomes obscured. At Niagara and for some distance 

 east and west it is marked by the Whirlpool quartzite, a hard, white 

 quartz sandstone 25 feet thick, which rests abruptly on the red Queenston 

 shales, as shown on the river above Lewiston or Queenston. This rock 

 shows beach cusps and other characters which indicate that the seashore* 

 was near. A. W. G. Wilson has interpreted this lens of sandstone as the 

 remnant of an old dune area reworked by the advancing sea, 66 and this 

 interpretation is favored by the character of the grains composing this 

 rock as well as by its distribution. Some of the bedding surfaces of this 

 quartzite show wave-marks closely resembling those of modern shallow 

 beaches, a feature repeated in a number of higher beds farther east. The 

 Whirlpool quartzite is not known at Eochester, where the contact be- 

 tween the Queenston and the Medina is again obscured, a condition which 

 practically exists throughout the rest of the area covered by these rocks. 

 The Whirlpool quartzite is thus seen to be a local formation apparently 

 unconnected with any direct eastern source. The section of the Medina 

 along the Niagara Gorge is as follows, 67 the Clinton or Sod us shale being- 

 included : 



Feet 



Super-formation. Clinton lower limestone (Wolcott limestone). 



8. Sodus shale. Olive green to grayish, sometimes purplish gray shale, 

 with occasional fossils especially Anoplotheca hemispherica and 

 A. plicatula and impressions suggesting Pterinea emacerata. Reed- 

 like impressions also occur 



( Abrupt contact. ) 



7. Thorold quartzite. Hard, massively bedded, compact, quartzose 

 sandstone, resembling the Whirlpool sandstone, and commonly show- 

 ing irregular cross-bedding, and showing in one place a couple of 

 beach cusps 15 feet apart with the central portion depressed nearly 

 2 feet below the crests. Sometimes a thin basal bed is separated 

 by a few inches of reddish shale from the main mass. Further 

 west in Ontario this rock carries Arthrophycus harlani 



'■•j 



86 A. W. (J. Wilson: Transact. Canadian [nstitute, vol. 7. pp. 139 186. 

 a7 A. W. Grabau: Hull. 45, N. Y. State Museum, pi>. 89-95, 



