GEOLOGY OF THE BROADALBIN QUADRANGLE 2*] 



Galway and at the edge of the Amsterdam reservoir. A fine ex- 

 posure of the coarse conglomerate occurs in the bed of the small 

 stream (wrongly placed on the map) one-third of a mile due north 

 of Barkersville. Other outcrops are one-quarter of a mile west of 

 the last named locality and along the creek one-half mile south- 

 west of Barkersville. 



A very similar conglomerate, at the base of the Potsdam, has been 

 described by Smyth^ as occurring at several points on Wells and 

 Grindstone islands in the Thousand Island region. Gushing^ has 

 also described a coarse conglomerate at the base of the very thick 

 Potsdam in Clinton county but there the rock is red and contains 

 much comparatively fresh feldspathic material. 



Three-fourths of a mile southwest of Barkersville, and along 

 the road, there is a large outcrop of typical Potsdam sandstone 

 which is gray, fine-grained, thin-bedded, and frequently ripple- 

 marked. In the creek one mile north-northeast of Mosherville 

 typical Potsdam sandstone is exposed and though no contact is 

 visible the rock doubtless comes against the Hoffman's Ferry fault. 



An excellent Potsdam section may be seen along the creek at 

 Edinburg. The section comprises chiefly typical looking sandstone 

 but there are certain notable variations. The lowermost layer ex- 

 posed (just below Latcher's falls) is a hard, gray, quartzitic rock 

 which greatly resembles the Grenville. This layer is practically 

 in contact with Grenville quartzite which may be seen in a very 

 small outcrop about one hundred feet below the falls. In the lower 

 portion of the falls there are two distinct beds of sandy conglom- 

 erate from one to three feet thick and containing pebbles as much 

 as one or two inches in diameter. Between the conglomerate beds 

 there is a distinct shaly layer containing the fossil shells of Lingula. 

 At the crest of the falls there are two or three thin layers of good 

 dolomitic limestone. The thickness of Potsdam below the high- 

 way bridge at Edinburg is estimated at from forty to fifty feet 

 with a general dip of from two to four degrees to the southeast. 

 Just above the bridge about ten feet of typical thin-bedded sand- 

 stones are exposed. 



A mile west of Edinburg, and on the same creek, is a large out- 

 crop of thin-bedded Potsdam sandstone in actual contact with the 

 Grenville. The lowest beds are dark gray, quartzitic, and look 

 much like the Grenville. The dip is 15 degrees to the southeast. 



Half a mile east-southeast of Northville are nutrerous exposures 



1 19th An. Rept. N. Y. State Geologist, 1899, p. 299. 



2 N. Y. State Mus. Bui. 95, p. 355. 



