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NEW YORK STATE MUSEUM 



east side of the fault, at a slightly lower level than the nearby 

 Little Falls, is an outcrop of the Theresa passage beds ; at the 

 south end, and unquestionably on the west side of the fault, Pots- 

 dam sandstone outcrops. Farther west outcrops are plentiful 

 on the west side of the fault but there are none on the east side. 

 The uncertainty in regard to the matter is whether the Theresa is 

 really on the east side of the fault ; a slight swinging of the northern 

 apex of the wedge toward the right would put it on the west side. 

 The uncertainty is regrettable; we can only say that everything we 

 saw in the field led to the confident belief in the relations as illus- 

 trated, and had not the Theresa exposure been forthcoming we 

 should have been forced to map it at that point owing to the testi- 

 mony of exposures a mile to the southwest. Nevertheless the drift 

 is very heavy and the mapping of a much faulted district such as this 

 must needs be very uncertain under the circumstances. 



Rock horses caught in along faults are common enough. But the 

 rock concerned is usually intermediate in age between the rock of the 

 upthrow and downthrow sides ; it has dropped relatively to the up- 

 throw side but has not dropped so far as has the downthrow side. 

 Such a wedge occurs in Saratoga along the Saratoga fault. But in 

 the case under consideration we have a small block about 350 yards 

 in length, which has dropped down along the fault zone some 300 

 feet more than the downthrow side has dropped. It is a diminutive 

 example of a trough fault. It is difficult to conceive of the me- 

 chanical conditions which would permit so small a block to drop so 

 deeply into the jaws of a fault. It may be the apex of a large 



dropped block, otherwise entirely eroded away. 



What seems to be another and similar case is found along the 

 Hoffmans fault a mile west of Porter Corners where a small block 

 of Little Falls dolomite lies in the fault zone closely adjacent to the 

 Precambric exposures to the west of the fault. To the east the 

 drift covers everything, but unless our attempted mapping is totally 

 at fault, the rock on the downthrow side should be the Potsdam sand- 

 stone. Certainly Precambric rocks come in on the east side of the 

 fault 2 miles away to the northeast. So we infer this to be a small 

 dropped block of the same type. 



As has been said, the mapping of the West Gal way fault across 

 the quadrangle is highly conjectural. There should be a fault 

 between the Precambric exposures south of South Corinth and 

 those of the Theresa at North Greenfield; there should be a fault 

 just west of the Potsdam exposures at Corinth, cutting them off. 



