178 R. I). SALISBURY EXTRA-MORAINIC DRIFT. 



gether probable that the bowlders seen between 1,000 and 1,100 feet 

 above tide are an index of bowlder-bearing clay existing here though 

 not exposed. 



Farther southward the same type of material occurs in the Pohatcong 

 and Musconetcong valleys. Lf well data may be relied upon, there is as 

 much as 70 feet of it in the valley near Washington, at an elevation of 

 about 400 feet. From the localities cited it will be seen that the vertical 

 range of the material is great within narrow geographic limits — fully 

 600 feet within six miles. 



Still farther southward, near High Bridge, at an elevation about equal 

 to that at Washington, or about 200 feet above the valley of the Raritan, 

 dose at hand, there is an exposure of about 30 feet of bowlder clay and 

 gravel. As at Oxford Furnace, the material is here partially stratified, 

 Imt a considerable proportion does not show any sign of orderly arrange- 

 ment, and the bowlders are disposed in the clayey matrix after the 

 fashion of true till. Bowlders five or six feet in diameter occur. One 

 bowlder, whose greatest dimension is fully 7 feet, is glacially striated over 

 nearly the whole of one face. As at Little York, so also here, one of the 

 ingredients of the bowlder clay is shale in large and small fragments. 

 Here also, as at Little York, it is difficult to find a piece of shale which 

 retains the form it possessed when deposited which does not show ice 

 scorings. In more than one instance bowlderets of shale were seen in 

 situ showing glacial markings with great distinctness, but which were so 

 far disintegrated as to make it impossible to remove them from their 

 position without their crumbling to fragments. Among the fragments 

 resulting from the disruption of shale bowlders pieces may be found 

 which retain portions of the original surface, and upon these stria? may 

 still be seen. The 4 matrix in which the stony material is imbedded is 

 locally of granite and crystalline schist origin — a sort of arkose. Its 

 abundance may perhaps be due in part to the decomposition of the 

 granitic material in the drift itself since its deposition. 



High Bridge is about fourteen miles from the moraine at its nearest 

 point. A few miles farther southwest ward, near Pattenburg, the phe- 

 nomena of High Bridge are repeated at a slightly greater elevation 

 But a single point of difference need be mentioned: the bowlder clay 

 here rests on shale, the surface of which beneath the drift gives evidence 

 of mechanical disturbance. 



Similar occurrences of bowlder clay are known south of Pattenburg to 

 a distance fully twenty miles south of the moraine. In all these places 

 the bowldery clay is essentially constant in chemical and physical 

 character, and whatever may lie the explanation of its existence in one 

 locality must he the explanation of it in all. 



