GEOLOGY OF THE NORTHERN ADIRONDACK REGION 359 



Van Ingen's study of the Saranac river section of the Potsdam, 

 extending along the river for 2 miles above and below Cadyville, 

 leads him to compute the thickness there shown at 1150 feet. 1 

 The w T riter agrees with him that there is no evidence of faulting 

 in this section, though he believes that it is terminated by a 

 fault at each end. Certainly one of the biggest faults in the dis- 

 trict, the Tracy brook fault, crosses the river somewhere between 

 the lower end of the section and Morrisonville, though apparently 

 with much diminished throw hereabouts. The Potsdam is a most 

 difficult formation on which to get accurate dip measurements, 

 and the writer's notes give the dip as somewhat less than that 

 stated by van Ingen, averaging about 5° instead of between 5° 

 and 10°, as given by him, which would cut down the above thick- 

 ness by some 300 feet. Whichever result be the more correct, the 

 thickness is impressive, since the basal beds do not show, nor 

 is the summit reached. Basal beds do indeed occur in the near 

 vicinity, showing in frequent outcrop on the higher ground a 

 mile south of Cadyville. These are on the strike of the river 

 exposures and at a higher altitude, yet belong much below them 

 stratigraphically, and the writer is disposed to the conclusion 

 that a fault intervenes between the two, likely a branch from the 

 Tracy brook fault. These beds show considerable thickness, and 

 it is thought highly probable that the thickness of the whole 

 Potsdam is more likely over, rather than under 1500 feet. 



The paleontologic and stratigraphic w r ork of Walcott and van 

 Ingen has shown that the upper portion of the formation, 

 through a thickness of some 350 feet, carries a sparse Upper 

 Cambric fauna. With the exception of a few supposed tracks, 

 of uncertain nature, no fossils have so far been found in all the 

 remainder of the formation, and there- is therefore an utter lack 

 of paleontologic evidence as to its age, and the possibility .that 

 the lower portion may be older than the Upper Cambric must be 

 conceded. But it seems to the writer that, fossil evidence being 

 lacking, the formation as it occurs in New York is not sus- 

 ceptible of subdivision. The basal rocks grade into those of the 

 middle division, as do those into the upper, and there is no 

 marked structural break at any horizon which would warrant 

 the assumption of any great difference in age between base and 



*Op. cit. p.532. 



