114 NEW YORK STATE MUSEUM 



lies about 30 feet above the dolomite, the basal layers of the under- 

 lying interval being unquestionably of the Black River group but 

 not so low as the Lowville and probably also younger than the 

 Watertown limestone. The Lowville is represented by 2-4 feet of 

 beds at Tribes Hill in the Mohawk valley, but here the crystalline 

 limestone is only 3, to 5 feet above it. The section at this locality 

 differs further in that it contains an unusual thickness (13 to iS 

 feet instead of 2 to 10 feet) of somewhat shaly limestone above 

 the crystalline bed before the Prasopora simulatfix fauna, 

 with which the typical Trenton begins in New York, sets in. This 

 irregularly distributed, presumably late Black River formation, in- 

 tervening between the true Trenton above and the more typical 

 Black River formations (Lowville and Watertown) beneath, will 

 be fully described in another paper. Here it will suffice to say that 

 it wedges out westwardly in the Mohawk valley before reaching 

 Little Falls. So far as known its maximum aggregate thickness is 

 about 60 feet, the lower 46 feet of which is exposed at Rock City 

 Falls. A good thickness is shown also in the section at Glens Falls. 



The work of Prof. W. J. Miller on the Broadalbin quadrangle 

 (next west of the Saratoga quadrangle) in 1909 shows that there 

 the Hoyt limestone is absent from the section, being replaced by 

 unfossiliferous dolomites and probably also by beds included in 

 an increased thickness of passage beds between the dolomite and 

 the Potsdam. 



The well drilled at the Hathorn spring in Saratoga a few years 

 ago is reported to have begun in the Trenton limestone and to 

 have passed through some 700 feet of limestone before reaching 

 the Potsdam. This is a thickness at least 300 feet greater than the 

 surface exposures indicate. The well is near a fault and it seems 

 probable that it crosses a branch of the fault in such wise as to re- 

 peat a considerable thickness of the limestone. 



Section at Whitehall 



Whitehall is between Saratoga and Ticonderoga and thus, from 

 the standpoint of distance, serves as a convenient intermediate point 

 between the two. The district is much faulted, but a good, con- 

 tinuous section is afforded from the Precambric up through the 

 Potsdam and well toward the summit of the Little Falls dolomite, 

 simply by ascending the hill known as Skene mountain, a fault block 

 whose summit rises sharply to more than 400 feet above the level 

 of Wood creek. Walcott has given a detailed section of the Pots- 



