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NEW YORK STATE MUSEUM 



overdeepening of the valleys has taken place that leads to exposures 

 of deeper beds surrounded by younger beds, a process ascribed by 

 some glacialists to glacial erosion. While on account of the con- 



Fig. 18 Diagrammatic section of a '' sink " or " cove ", the black line indicating the 

 subterranean water course 



siderable depth of most of these lakes, there is no doubt that their 

 bottoms reach clown even into Siluric beds when their shores are 

 in the Devonic, but the maps do not suggest this fact, except in a 

 very few instances. One of these that appears quite convincing 

 is the exposure of Middlesex black shale along the west branch 

 of Keuka lake 1 and in the lower portion of the valley lying in 

 the continuation of the lake [see text fig. 19]. This long out- 

 crop of Middlesex shale is entirely isolated and surrounded by the 

 overlying Neodevonic beds (Cashaqua shale, etc.) In this case it 

 would seem that the north-south flowing brook, emptying at 

 Branchport, and running with the dip of the rocks* found itself in 

 the condition described above under corrasion inliers and thus 

 might have alone been competent to produce a -part of the inlier, 

 although its short length and small size and the great length of the 

 inlier and depth of lake basin indicating a great amount of erosion, 

 are now entirely out of proportion and glacier ice is therefore to 

 be appealed to as a factor, especially in regard to the inlier of the 

 west branch of the lake. 



We have thus far considered the inliers which originate from 

 the agency of water, in either depositing or eroding. We now 

 turn to the more important groups of inliers produced by diastro- 

 phism. These are the fold and fault inliers. 



3 Fold inliers. These are formed a on the summits either of a, 

 normal anticlines or a., domes (" uplifts," " parmas ") or b through 

 overturned folds (" Klippen "). 



We will first consider those very frequent cases of inliers of 

 rocks, appearing on summits of normal folds through erosion. 



1 Luther, D. D. Penn Yan-Hammondsport Quadrangles, N. Y. State Mus. 

 Bui. 10 1. 1906. 



