GEOLOGY OF THE VICINITY OF LITTLE FALLS 29 



4 the contact on the south side of the river at Little Falls is 

 excellently shown. The lower layer is quite pebbly and extra 

 sandy, as it is at Spruce creek, but the basal layer at Spruce 

 creek, because of overlap, is from 150 to 200 feet above this pebbly 

 layer at Little Falls. It is unlikely that this latter represents 

 the actual base of the formation and a reference to the Potsdam 

 because of lithologic character seems wholly uncalled for in view 

 of the above facts. 



The contact with the overlying Lowville limestone is shown at 

 numerous localities within the map limits, and at many others 

 shows within a few feet. A number of the tributary creeks into 

 West Canada creek, both above and below Middleville, expose this 

 contact. Some of the creeks into the Mohawk from the south 

 also expose it, and it is well shown about Ingham Mills. A 

 comparison of these different contacts brings out some interest- 

 ing things in regard to the presence or^absence of the passage 

 beds, and variations in thickness of the Lowville. down to com- 

 plete absence, going to show great local variation in deposition 

 conditions at this horizon, and indicating, when coupled with the 

 occurrence of the local conglomerate at the summit of the Beek- 

 mantown, a probable slight unconformity. 



Trenton formation. The Trenton formation as mapped is made 

 to include the Lowville and Black river limestone stages as well 

 as the Trenton limestone, since in the district these are mainly 

 too thin and too variable to be mapped separately from the 

 Trenton without exaggeration. They lie below the Trenton and 

 can in general be assumed to represent the basal 5 to 15 feet of 

 that formation as mapped. 



Lowville limestone. The different beds of this formation are 

 very similar, consisting of gray, brittle, pure limestone layers in 

 which are more or less numerous long, tubular cavities filled with 

 white, crystalline calcite, which are exceedingly characteristic of 

 the formation. Other fossils are very rare, though Leperditia, a 

 fossil crustacean shell looking like the half of a small bean, occurs 

 occasionally. It is the purest limestone in the district, is fairly 

 thick bedded, and has therefore been considerably quarried for 

 building stone for local use. 



