﻿REPORT OF THE DIRECTOR TOJO T^ 



About three-fourths of the quadrangle has been covered and, thus 

 far, the rocks are all of Precambric age. A well-defined and here- 

 tofore unnoted outlier of Paleozoic rock (Potsdam sandstone and 

 Little Falls dolomite) has been found just south of the sheet and 

 one mile west of High Street village. 



The Grenville formation is present to an unusual extent, making 

 up nearly 50 per cent of the area so far studied. Limestone occurs 

 in abundance and with it is associated an extensive mass of horn- 

 blende gneiss. Other common Grenville rocks are : quartzites, gray 

 garnet gneisses, white feldspar gneisses, and graphitic schists. 

 Almost without exception the Grenville occupies the valleys. 



No less than four ages of igneous rocks — all younger than the 

 Grenville — have been observed. Of these the syenites and asso- 

 ciated rocks are by far most prominent. The greenish gray rather 

 quartzose syenite often grades into a pink medium-grained biotite 

 granite on one hand and into a gray coarse-grained, very porphy- 

 ritic granite on the other. These syenites and granites have broken 

 through the Grenville in a very irregular manner so that the geologic 

 map will present a decided " patchwork " effect. 



Large dikes or small bosses of gabbro cut both the Grenville and 

 the syenite-granite series. No less than forty of these dikes have 

 already been mapped and the rocks show but little sign of meta- 

 morphism. Pegmatite dikes are common and the}- have been found 

 cutting the gabbros in many places. 



The youngest rocks of the district are in the form of diabase dikes 

 which are known to cut all the other formations, even the pegma- 

 tites. The rocks are generally much finer grained and the dikes are 

 fewer in number and usually smaller than the gabbro. 



The region has been subjected to rather extensive normal fault- 

 ing and a number of these faults have been mapped. The strike 

 of the faults varies from northeast-southwest to northwest-south- 

 east. 



The topography is almost wholly dependent upon rock character 

 and structure. Because of several favoring conditions, exfoliation 

 domes (syenite or granite) form a striking feature of the landscape. 



The glacial phenomena are also of interest. Many glacial striae 

 have been observed and in no case do they vary more than twenty 

 degrees from due north and south. A fine example of a glacial 

 lake (Lake Warrensburg) formerly covered all the lowland area 

 around Warrensburg and had arms which extended for several 

 miles up both the Hudson and the Schroon rivers. Another con- 



