GEOLOGY OF THE VICINITY OF LITTLE FALLS 57 



The Beekmantown at Little Falls is 450 feet thick. Northward 

 from there, following first the fault line and then the Beekman- 

 town-pre-Cainbrian boundary, the thickness gradually diminishes. 

 At Diamond hill it has shrunk to about 100 feet. Beyond that 

 point exposures are not sufficient to determine the amount ab- 

 solutely, since the base novrhere outcrops. The last Beekman- 

 town exposures seen are located nearly 2 miles south of the north 

 boundary of the map sheet. While the thickness here can only 

 be inferred, it can be safely said that it can not exceed 40 feet, 

 and is likely not over half that amount. 



One mile farther to the northwest Trenton limestone and pre- 

 Cambrian gneisses are exposed sufficiently close to one another 

 to almost preclude the possibility of the presence of the Beekman- 

 town. Darton has however mapped it as extending some three 

 or four miles farther to the northward. The writer has not been 

 over the ground in that direction and does not know whether 

 Darton's mapping there is based on actual outcrops or on infer- 

 ence. Tn either case we are here near the point of disappearance 

 of the Beekmantown, beyond which the Trenton overlaps it on 

 the pre-Cambrian. 



There is an exceedingly interesting section at Diamond hill, 

 demonstrating a local overlajD of the Beekmantown there, which 

 may be taken as illustrative of the whole process. As has already 

 been stated, there is an exposure of the contact of the Beekman- 

 town on the pre-Cambrian in the bank of Spruce creek at Diamond 

 hill. Here the top of the pre-Cambrian is at an elevation of 1280 

 feet above sea level. But only a few rods to the northwest is a 

 low knoll, all over which pre-Cambrian rocks are exposed, which 

 reach an elevation of 1360 feet. Plainly we are here dealing with 

 a low pre-Cambrian knob or hillock at least 80 feet in original 

 hight, around which the Beekmantown was deposited before over- 

 topping it. Sixty rods west of Spruce creek a little brook comes 

 down which exposes a most interesting section of Beekmantown 

 rocks some 25 feet in thickness. Then follows a gap of 25 yards 

 in which are no exposures, after which are abundant outcrops of 

 pre-Cambrian gneisses, the nearest to the Beekmantown rocks 

 beins: at least 15 feet above them in elevation. That there is no 



