﻿GEOLOGY OF THOUSAND ISLANDS REGION 7 



The area is one of low altitude and comparatively little relief, 

 forming the west end of the plain which borders the entire north 

 front of the Adirondack highland, and merges hereabouts into 

 the north end of the Black river lowland. To the southward 

 the altitude considerably increases and a bit of the high Trenton 

 escarpment which forms the west wall of the larger part of the 

 valley of the Black river, appears in the extreme southwest 

 corner of the Theresa sheet, reaching an altitude of over 800 

 feet, the highest elevation in the mapped district. Altitudes con- 

 siderably in excess of this appear not far to the southward on the 

 Watertown sheet. But with this one trifling exception the high- 

 est elevations in the mapped area but little exceed 600 feet 

 (this in the southeast corner of the Theresa sheet) and thence 

 drop gently to the north and west to the level of the lake and 

 river (246 feet). 



Though the district is thus moderately flat, the local relief is 

 considerable, in minor fashion. Ridges and valleys characterize 

 the districts underlaid by Precambric rocks. The flat-lying 

 Paleozoic rocks form plains which are fronted by steep cliff 

 escarpments. In both cases abrupt changes of level of from 50 

 to 100 feet are quite common. These features also are most 

 pronounced in the eastern part of the area and fade out westward, 

 so that but little relief is manifested on the Cape Vincent and 

 the larger part of the Clayton sheet. 



With the exception of the St Lawrence, the Black and Indian 

 rivers are the only streams of respectable size within the mapped 

 area. Most of the streams flow in narrow, steep walled valleys, 

 and no deep, broadly opened valleys have been detected. There 

 are many features of interest in the minor drainage to which 

 attention will be directed later on. The group of lakes of an 

 unusual type forms a very prominent feature. Several of these 

 lakes may be noted near the eastern edge of the Alexandria sheet 

 and there are a few more beyond the map limits. They are not 

 a usual feature of this part of the State. Their presence and 

 their very localized distribution require explanation. 



Glacial deposits are in small bulk in the district and much bare 

 rock appears, with wide areas where the soil is very thin. In 

 the limestone districts the streams show a tendency to go under- 

 ground and bared limestone surfaces show considerable amount 

 of rock removal through solution along the joint planes. 



The district is largely one of small farms. Little or no forest 

 remains on it, though there is much waste land. The largest 



