Cusiiing — Geology of Clinton County. 



557 



the south into Peru, and well to the north also. We may call it the "Pitts- 

 burgh fault." Just north of Bluff Point, the east and west fault, already 

 described, runs out to meet it. The throw of this, which may be called the 

 " Bluff Point fault," is to the north, and an approximation to its amount may 

 be had. The entire upper division of the Chazy, 200 feet thick on Valcour 

 island, fifty to 100 feet of the middle division, and fifty to 150 feet of the 

 Trenton are missing, so that the vertical displacement is from 300 to 400 feet. 

 North of this fault, the Plattsburgh fault is not traceable for nearly four 

 miles, on account of the total lack of exposures, but north of Plattsburgh 

 city, on the prolongation of the fault line, is a displacement which is thought 

 to be the same. Here the Chazy exposures on the Avest side are sharply cut 

 off at an angle with their strike. To the east no rock is exposed for a 

 distance of one mile and a half, when the Cumberland head slates come in. 

 Though the faidt line is strongly marked wherever shown, no data are 

 available for determining the amount of displacement. The throw is to the 

 east, and must be large. 



Three-fourths of a mile to the west is another great fault, very well 

 shown, which brings up the Calciferous against the Chazy. The horizon in 

 the Calciferous has not been determined, but is apparently well down, so that 

 the entire lower division of the Chazy, over 300 feet thick, and probably a 

 much greater amount of the Calciferous, are faulted out, the throw again 

 being to the east. This fault may be named the " Beekmantown fault." 

 It has a more easterly trend than the Plattsburgh fault, so that the two 

 appear to effect a junction on the Beekmantown line, shutting out the Chazy 

 altogether, and bringing the Calciferous and Cumberland head series into 

 contact in southern Beekmantown. The displacement here, therefore, must 

 be very great, as the entire Chazy, all the ordinary Trenton, and an unknown 

 amount of the Calciferous are missing, and 1,500 feet would be a very 

 moderate estimate of its amount. 



These three, together with the cross-fault in the Chazy beds between the 

 Plattsburgh and Beekmantown faults, are the main faults in the township. 

 Small faults occur on Cumberland head, and the slaty cleavage there 

 developed in the whole series would probably be represented by a con- 

 siderable fault, were the beds more rigid. X<> doubt other faults occur, 

 but the paucity of outcrops renders their discovery and decipherment nearly 

 impossible. 



Series V. Only two dikes have been found in the township, but they 

 are of interest as, together with the South Hero dikes described by Kemp, 



