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NEW YORK STATE MUSEUM 



hill, where stream flow occurred either side of an ice block, 

 which filled and protected the valley bottom, are to be ex- 

 pected in the Mohawk valley; along with the consequent pond- 

 ing of the waters in side valleys and delta fillings. However, 

 the writer's task of tracing the high glacial waters of western- 

 central New York, in their flow past the receding ice front, 

 around into the Mohawk valley with free course to the sea, is 

 here completed. 



It may be noted that the eastward flow of ihe waters proves 

 thai; there was at this time no ice blockade in ihe lower Mohawk 

 region. 



MOHAWK VALLEY FEATURES 



Barrier at Little Falls 



Structure 



The critical element in the drainage phenomena of the upper 

 Mohawk valley is the rock barrier at Little Falls. Even the 

 casual observer on the railroads must have noticed the narrow 

 rocky gorge and the palisade character of the lower walls. 

 The latter feature is partly artificial in places, as the lower, 

 narrow gorge has been much cut to give room for the Erie 

 canal and three railroads. The locality is interesting in itself, 

 apart from its relation to the glacial waters, and it merits 

 description. 



The existence of this rock barrier at Little Falls is due to a 

 great fault, the most westerly of a series of ancient faults 

 which lie athwart the lower Mohawk valley from Little Falls 

 eastward to Kotterdam, 1 and which produce the narrow places in 

 the valley and the bold east-facing cliffs at several localities. 

 Like the other faults, this one has the upthrow side on the 

 west, thus forming a great scarp or steep slope of hard rocks 

 facing east. The-upthrow carried high into the air the strata 

 of the region (TJtiea shale, Trenton limestone, and Calciferous 

 sandrock) and even brought well up to view the Archean crys- 

 tallines ^augite syenite of the state map). Erosion has re- 

 moved all the clastic rocks and has left the crystallines ex- 

 posed at the valley bottom for a width of over half a mile. 



1 See description by N. H. Darton in 14th An. Rep't N. Y. State Geol. 1894. 

 p. 35. These faults are plainly indicated on the Geologic Map of New York 

 by F. J. H. Merrill, state geologist, 1901. 



