GEOLOGY OP THE NORTHERN ADIRONDACK REGION 377 



are left in doubt as to how large a portion is shown, and whether 

 or not a fault intervenes between the Trenton and Utica, as is 

 very likely. Faults so abound in the Champlain region that the 

 finding and measurement of complete sections is a matter of great 

 difficulty, so abound in fact that the geologist is more often called 

 on to demonstrate their absence than their presence. If there is 

 none here^ the Trenton has obviously thinned greatly southward. 



In the country between Lake Champlain and the mouth of the 

 Mohawk, exposures of the formation are interrupted and frag- 

 mentary. At Glens Falls Prosser has measured several Trenton 

 sections, but all terminate in that formation, so that the full 

 thickness is not shown.i The greatest measured thickness in the 

 vicinity is 63 feet, the basal portion consisting of very massive, 

 black, fine grained beds, while above is much thinner bedded 

 material, with some intercalation of gray, crystalline layers. If 

 the total thickness were much greatei: than that shown in this 

 section, it would seem that thicker sections would surely be forth- 

 coming, and their nonappearance seems therefore significant. No 

 passage beds seem to have been noted, but whether their absence 

 is due to nonexposure of the proper horizon or not, is not clear. 



Similarly, about Saratoga, Prosser's sections show a maximum 

 measured thickness of 37^ feet for the Trenton, mostly thin 

 bedded, but some massive, and here again the summit is not 

 exposed, so that the entire thickness may be in excess of that 

 amount, but is not likely to be greatly in excess [pl.6]. 



While the sections at these two localities are not decisive as to 

 thickness, it seems probable that the entire amount can not greatly 

 exceed the figures given, and hence that the formation has rapidly 

 thinned in this direction. 



In the lower Mohawk valley, in the Amsterdam-Hoflfman region, 

 Prosser and Cuming's sections afford accurate data concerning 

 the formation.2 They show considerable variation in thickness, 

 the maximum amount being 36^ feet in the section at Morphy's, 

 while the minimum is 20 feet. The lower 6 to 8 feet are of 

 massive, often crystalline, limestone, while the remainder con- 

 sists of thinner bedded and dark colored, more shaly material. 



^X. T. state Mus. Bui. 34, p.4S0-S2, pl.8. 



=15th An. Rep't State Geol. p.647-59 ; N. Y. State Miis. Bui. 34, p. 419MM. 



