

GEOLOGY OF THE SCHROON LAKE QUADRANGLE 87 



except at the four places indicated on the map. A little west of 

 the middle of this area, there is an area of nearly a square mile, 

 mostly an old clearing, where a boulder moraine is conspicuously 

 shown. 



In the area of Pleistocene east and southeast of Olmstedville 

 morainic and fluvio-glacial deposits are also well exhibited, with 

 >oulders especially prominent in the northern half. In and near 

 Olmstedville, in the area of Grenville, there are also fine develop- 

 ments of .morainic and fluvio-glacial materials with boulders 

 common. 



Very conspicuous boulder morainic deposits occur for a mile on 

 either side of the Trout Brook valley from I to i l / 2 miles south- 

 east of Muller pond. 



The Pleistocene of the area between South Schroon and Grove 

 Point is largely morainic material. 



Among many smaller scale morainic deposits are those in the 

 valley east of Catamount hill, and three- fourths of a mile south- 

 west of Irishtown. 



Glacial boulders (erratics). Glacial boulders or erratics are 

 very abundant and widespread over the quadrangle, though they 

 are much less common on the tops of mountains and hills than over 

 the lowlands. Some of the more prominent groupings of boulders 

 in so-called " boulder moraines" are mentioned above. In addi- 

 tion to those there should be noted the accumulation of hundreds 

 of large and small angular masses of Potsdam sandstone just south- 

 west of Thurman pond and all over the area of Potsdam sand- 

 stone north of the pond. 



An 8-inch angular fragment of typical Trenton limestone was 

 noted a few rods west of the south end of Thurman pond. This 

 suggests either a hidden ledge of such rock in this portion of the 

 Schroon valley, or a mass scraped off and broken up by the ice, 

 though the fragment might possibly have been carried by the ice 

 for many miles. 



While numerous boulders represent various types of the region, 

 most of the largest ones are of Marcy anorthosite. The writer 

 was particularly impressed by many boulders, usually only moder- 

 ately rounded, ranging from 10 to 20 feet in diameter in the woods 

 on the southern portion of Texas ridge. 



A very large and interesting glacial boulder of Marcy anorthosite 

 lies in an old field near the southeastern base of Cobble hill three- 

 fourths of a mile southwest of Warren's hotel. Roughly meas- 



