NEW YORK STATE MUSEUM 



project into the Niagaran Rochester shale. One may then find, on 

 abraded surfaces, as at Lockport, the lens contrasting as a white 

 inlier with the dark shale [see text fig. 6, /]. 



2 Erosion inliers. We distinguish in this class between corra- 

 sion inliers which have resulted from river corrasion ; solution 

 inliers ; and glacial erosion inliers in which the ice is thought to 

 have been the exposing agent. 



Jefferson county, N. Y. Scale i m. == i in. 



(7 Corrasion inliers. The first group we have found excellently 

 exemplified in small and simple forms in the southern portion of the 

 Clayton sheet. As the sketch maps inserted indicate [sec text 

 fig. 8, 9, io], these inliers consist of strips of Lowville limestone ex- 

 posed along brooks and surrounded on all sides by Black River 

 limestone. The conditions which have produced this peculiar form 

 G f inlier — which judging from our maps is very rarely seen in 

 other parts of the State — are the following: The coincidence 

 of the dip of the beds and of the course of the brook and a resist- 

 ance of the underlying Lowville limestone to erosion that is greater 

 than that of the Black River beds. The brook, as a rule, reaches 

 the inlier by a fall and finally leaves it by very gradually passing 

 again upon' the overlying rock [see text fig. io, p. 172]. That 

 means that for some distance the gradient of the brook is 



