FEATURES OF TRAP EXTRUSIONS IN NEW JERSEY 321 





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and there is another feature of especial interest. The slaggy, wrinkled 

 crust of one of the flows is finely exposed in two or three places. It 

 projects as an inclined shelf, one or two feet wide and fifteen or eigh- 

 teen feet long, from under later trap, but at only two or three places 

 on this shelf is the structure perfectly developed. The wrinkled 

 surface is shown in Fig. 15. It 

 appears to be a crust one-half to 

 two inches thick, over another 

 flow which also shows a wrinkled 

 surface in one place. Although 

 somewhat weathered the original 

 rock was plainly of a close, glassy 

 texture. No vesicles are visible. 

 The wrinkles are plentiful, form- 

 ing curved grooves one-fourth to 

 one-half inch deep. The direc- 

 tion of all of them points to a flow northward at this point, 

 and though we must not lay too much stress upon this, a north- 

 ward flow is perfectly consistent with the shape of the valley. This 

 crust does not of course represent a part of the final surface of the 

 lava flow. It is merely the crust of one of the small sheets, spurted 

 forth under pressure, and soon covered by other portions of the flow. 

 The innumerable bowlder-crusts to be found throughout the area 

 which we are studying are practically the same thing, but in few cases 

 was the wrinkled surface preserved so perfectly as in this example. 



At the Falls the rocks on both sides of the river at the brink of the 

 chasm show many irregular vug holes and in places crystals can be 

 seen. We are here, however, far above the base of the sheet and the 

 exposure is not a typical one. Farther south there is an occurrence 

 on the Little Falls turnpike, showing the characteristic structure. 

 The most noteworthy feature is the recurrence here of the wrinkled 

 crust of one of the bowlder masses, showing as a slight projection. 



Next comes the West Paterson quarry already described in detail. 

 I have found in this vicinity evidences of the lake valley over a large 

 surface area but have not yet had the opportunity to explore the 

 vicinity in sufiicient detail to fix definitely the limits of the area covered 

 by the lake. 



