46 NEW YORK STATE MUSEUM 



Precambric surface lies at about five hundred feet. The Precam- 

 bric on the west side (Fraker mountain) of the fault rises to over 

 fifteen hundred feet so that, disregarding subsequent erosion, the 

 amount of displacement near the map edge is approximately one 

 thousand feet. Dolomite was formerly exposed near the road one 

 mile northeast of Edinburg. Black shale fragments may be seen 

 along the road one-half mile north of Edinburg and this suggests 

 that shale may now exist under cover of the drift or a small shale 

 mass may have been completely removed by ice erosion. 



The second and much smaller fault passes just north of Edin- 

 burg and strikes a little to the north of east. Its exact location 

 and relations are rather obscure, except that the upthrow side 

 is on the south and at the village are excellent exposures of Pots- 

 dam sandstone dipping toward the southeast. 



Hoffman's ferry fault 



This has long been known as one of the greatest Mohawk valley 

 faults and as usual the upthrow is on the west. Just north of 

 Hoffman's Ferry (on the Mohawk river) the displacement is esti- 

 mated at 1300 feet by Cumings 1 and at 1600 feet by Prosser. 2 



Where this fault enters the Broadalbin quadrangle, one and 

 three-fourths miles southwest of Galway, Black River-Trenton 

 limestone may be seen sharply faulted against the upper portion of 

 the Theresa formation and the amount of displacement is esti- 

 mated at two hundred and fifty feet. The limestone is in the form 

 of a narrow wedge crowded against the fault plane and showing 

 varying dips. One-half of a mile west-northwest of Galway lower 

 dolomite beds containing chert are faulted against lower beds of 

 the Theresa formation and the displacement is about equal to the 

 height of the hill here, or two hundred feet. East of North Galway 

 the dolomite comes against the Precambric so that the displacement 

 is about two hundred and fifty feet. [See fig. 7.] The occurrence 

 of the small separated masses of Precambric against the fault in 

 this vicinity is due to the faulting and later erosion of the scarp. 

 A mile north of Mosherville Potsdam sandstone outcrops in the 

 creek with Precambric a little to the north. The relations of the 

 fault are here not clearly shown but judging by the elevation of 

 the Precambric just to the north, the throw is probably in the 



*N. Y. State Mus. Bui. 34, p. 450. 

 2 he. cit. p. 476. 



