90 XEW YORK STATE MUSEUM 



while not seen is clearly indicated . by the presence of Potsdam 

 sandstone in the cut of the Delaware and Hudson Railroad south 

 of McKenzie creek, close to and below the topographically much 

 higher Precambric rocks, as also by the much increased dip (io°) 

 of the sandstone. One cross fault is directly exposed in the Port 

 Henry block in ^IcKenzie creek just below the highway bridge, a 

 little east of the Y of the ^NlineWlle Railroad. This fault strikes 

 n. 5^ e. and separates a white Potsdam sandstone on the west from 

 a more massive pink sandstone with distinct cross bedding. The 

 latter represents the older bed and the downthrow seems to be to 

 the west of the fault plane. Several smaller cross faults are well 

 exposed to the north of the railroad tunnel north of the village. 

 One of these (striking n. 60° w.) shows a drop of only 2 feet to 

 the north, which, however, is finely shown by the shifting of a 

 bed of black chert in the dolomite. 



The Westport block is bordered on the south by a transverse 

 fault, striking n. 50'' e. whose fault inscarp (here Potsdam) is well 

 exposed in the woods above the railroad track. In the railroad cut 

 itself the Potsdam is seen abutting against the Precambric rocks. 

 Another cross fault is to be inferred to again separate this Potsdam 

 block from the Trenton beds adjoining to the north of it along the 

 deep depression of the lower course of ^lullen brook. Still another 

 cross fault, running in northwestern direction, cuts off the Potsdam 

 and Beekmantown rocks from the anorthosite at the northern out- 

 skirts of the village of Westport. 



While thus the boundaries of these two Paleozoic areas that ap- 

 pear as embayments in the eastern Adirondacks are formed by 

 fauhs, except in the east where the rocks dip under the waters of 

 the lake, the physical character of the rocks and their relation to 

 the underlying rocks bear intrinsic evidence of their formation in 

 shallow water and not ver\- far away from shore lines. This is 

 especially true of the Potsdam sandstone, which forms but a thin 

 veneer on an irregular surface in the southern part of the Port 

 Henry area, so that in several places hillocks of Precambric rocks 

 penetrate the sandstone beds. 



In the Westport area the prevailing dip is to the west and south 

 of west, showing that the fault block is tilted toward the master 

 fault. At the base of the fault scarp the dips of the Beekmantown 

 beds are steeply to the east, owing to the dragging. Low folds and 

 cross faults cause locally divergent dips as at the mouth of Ham- 

 mond brook at Westport and at several places on the shore south 



