﻿GEOLOGY OF THOUSAND ISLANDS REGION 153 



plucking on the limestone ledges; which previously had been at- 

 tacked from the northward. 



The massing or localization of the drift ? so unlike anything else- 

 where in the southern half of our area, suggests that it was the 

 accumulation produced by a readvance of the ice margin, and was 

 followed by a retreat of the ice front to the latitude of Clayton, 

 where the glaciers made another stand, or readvance, with accumula- 

 tion of another belt of heavy boulder moraine (or boulder kame) in 

 the Clayton-Lafargeville-Redwood moraine. 



Boulder kames. The glacial deposits with sharpest relief and, 

 outside the Black river moraine, the most conspicuous masses are 

 the detached or isolated hills of boulders and cobbles which fall 

 in this class. With little attempt to classify the drift forms these 

 would be called bouldery moraine, but on account of the predomi- 

 nance of water-worn materials in the hills and on their flanks, and 

 their isolation, it is thought best to distinguish them as a form 

 between true moraines and typical kames. They stand out isolated, 

 apart from any line or ridge of moraine, being the most striking 

 hills of their neighborhoods. One known as the " Hogsback " lies 

 iV 2 miles northeast of St Lawrence and 4 miles southwest of Clay- 

 ton and is over 100 feet high. Four smaller but conspicuous coni- 

 cal hills lie in chain ? in the line of ice flow, in esker-kame fashion, 

 forming the river front of Prospect Park, west of Clayton. These 

 are shown in plate 46. The same map shows the striking group 

 of cobble hills 2 miles north of Lafargeville, having an east-west 

 distribution and somewhat morainic aspect, which have supplied the 

 materials for the best display of Gilbert bars in the entire area 

 [pi. 49-53]. On the edge of this map and reaching over on the 

 Alexandria sheet [pi. 47] is another prominent hill, called Pine 

 Grove hill, 5 miles northeast of Lafargeville and nearly 4 miles 

 southwest of Plessis. Very heavy cobble bars of Gilbert waters 

 are thrown north and south from this hill, shown in plates 45, 46. 

 A pit for gravel has been dug on the summit of the hill. Yet an- 

 other hill of this kind is shown on plate 47, Y\ mile northwest of 

 Redwood. There is a chain of similar hills all along the north side 

 of Grindstone island. 



From the large amount of rounded or water-transported materials 

 in these hills, their isolation and their form and alinement, it ap- 

 pears that they were built, at least in larger part, by torrential 

 streams. And as all the area was buried under deep waters of 

 Lake Iroquois during the ice waning it would appear that the 

 streams must have been surficial to the ice sheet and have poured 



