ELIZABETHTOWN AND PORT ITENRY QUADRANGLES 89 



sunk in deeply between the overtowering mountains of harder 

 Precambric rocks. 



The physiography of the Precambric mass of the Adirondacks 

 is, according to Professor Kemp's investigations, mainly controlled 

 by block faulting with the structure lines running principally in 

 northeastern direction. Likewise, the Plattsburg area of Paleozoics 

 has been found by Professor Gushing and others to possess as 

 the main factors of its structure a number of meridional faults 

 with connecting cross faults. 



The Port Henry and Westport areas are identical in structure 

 with the larger northern Plattsburg area. They are both, in the 

 main, sunken blocks bounded on the west by distinct fault scarps 

 where the harder Precambric rocks project above the less resistant 

 Paleozoic rocks. This fault scarp is easily recognized in a vertical 

 cliff that crosses the northern part of the village of Port Henry; 

 and it is still more prominent in the Westport embayment where 

 for at least 6 miles it forms a bold escarpment separating the 

 wooded Adirondack region from the fertile shore plain in front 

 of it. 



The fault contact can be observed in several places in both areas. 

 At Port Henry it is well exposed on the north side of Lock Lane 

 where it is seen to dip steeply (50°) to southeast, and still better 

 under the bridge of North Main street over Mill brook at the north- 

 ern outskirts of the village. Here the Grenville limestone comes in 

 contact with the reddish Potsdam sandstone along a northeasterly 

 striking fault, the sandstone being dragged up along the fault plane 

 and representing the downthrow. While in the Westport embay- 

 ment the contact is not directly shown, in several places, as at 

 ^lullen brook, in the Stevenson (Elm brook) farm and northeast 

 of Westport village, the Beekmantown rocks are exposed a few 

 rods from the high bluffs of Precambric rocks to the west, the 

 steep local dip of the dolomite at the same time indicating the close- 

 ness of a line of profound disturbance. 



These meridional faults emerge from the Precambric rocks in 

 the south and disappear again in them to the north. The north 

 and south boundaries of the Paleozoic areas are mainly formed by 

 cross faults. In the Port Henry block which has a triangular form 

 the master fault, forming the western leg of the triangle, runs in 

 northeasterly direction and plunges into the lake in Craig harbor 

 while the other leg is formed by a northwesterly fault, both inter- 

 secting near the first Y of the Mineville Railroad, where the Pots- 

 dam reaches its maximum altitude in this area. The latter fault 



