﻿I48 NEW YORK STATE MUSEUM 



chapter in connection with the stratigraphy [p. 129]. The valley 

 and scarp topography is certainly older, at least in great part, than 

 the latest glaciation. 



Plains of deposition. Flat stretches of detrital deposits occupy 

 the valleys and basins in the northern part of our area and the low- 

 lands in the southern part. They are broadly developed over the 

 southwestern part of the area, covering nearly all of the Cape Vin- 

 cent sheet and a large part of the inferior levels of the Clayton sheet. 

 Doubtless the more elevated of these detrital plains have rock floors, 

 those about Lafargeville and Clayton for instance, but the rock is 

 masked; while the valley and basin fillings are deep clay. 



These plains are chiefly clay, though sometimes sandy silt and 

 occasionally sand. They represent the distributing and leveling 

 work of standing waters, Lake Iroquois and Gilbert gulf, and are de- 

 scribed with reference to origin in a later chapter, page 156. The 

 best example of the sand plains may be seen 3 miles southwest of 

 Theresa, crossed by the Clayton branch of the New York Central 

 Railroad between Theresa Junction and Strough. Beyond this, both 

 east and west of Lafargeville, the plains are clay. From the trains 

 on the Cape Vincent branch of the railroad the clay plains may be 

 seen spread far and wide, as flat as a prairie, all the way from 

 Limerick to Cape Vincent, with a few interruptions of rock or of 

 till ridges. 



The more extensive, upland clay plains shade off into till, while 

 some of the valley clays are conspicuously pitted, as if deposited 

 over ice [p. 158, pi. 47]. 



Lake basins. Perhaps the most puzzling of the physiographic 

 features are the basins or basinlike valleys with steep rock walls. 

 These are more striking in the district of Potsdam and Precambric 

 rocks of the Alexandria quadrangle, where they hold an interesting 

 group of lakes, the only lakes in our area, excepting Hyde and 

 Perch lakes on the Theresa quadrangle. The five lakes of our 

 area, near Redwood, shown in plate 47, are only the western mem- 

 bers of a large group. Some basins without lakes and some steep- 

 walled valleys in limestones on the Theresa and Clayton sheets are 

 probably of similar genesis. 



Two facts in connection with these basins are specially to be 

 noted, the steep, scarplike rock walls and the very small amount 

 of glacial drift. These features seem abnormal in a district that 

 has been subjected to probably repeated glaciation. While these de- 

 pressions are mostly oriented in general harmony with the physio- 

 graphic alinement of the region, having a northeast-southwest atti- 



