TKIASSIC. 525 



composed of fragments derived from them plus a small contribution by shore currents. Allow- 

 ance can be made for the work of the currents, but the widespread dissimilarity of constitution 

 is due chiefly to the faulting which has occurred. The waves of the sea in which the Newark 

 beds were deposited did not on the northwest border in general beat against the rocks which now 

 adjoin this area. 



The relation of the conglomerates to the shales is also significant. They do not form a single 

 horizon which may be used in interpreting the structure. Instead, they grade either into 

 argillaceous shales, or black argillites, or arkose sandstones. Time and again the pebbly layers 

 were seen to appear in the shales and to increase in thickness and numbers until they become 

 massive conglomerates. 



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The trap rocks of the Newark beds in New Jersey and New York have been described more 

 or less in detail by several geologists, and it has been demonstrated that overflow sheets, intrusive 

 sills, plugs, and dikes occur. 



The most important of the overflow sheets are the three concentric ridges forming the 

 Watchung Mountains. These sheets are to all appearances strictly conformable, both to the 

 underlying and to the overlying shales. Nowhere is there any indication that the trap breaks 

 across the sandstone or shale layers. Wherever the basal contact is exposed, and exposures 

 several hundred feet in extent are known, the trap is seen to follow exactly the bedding plane of 

 the shales. 



Moreover, the extensive metamorphism of the associated sedimentary beds, a marked 

 feature in the case of all the intrusive sheets, is entirely absent. Locally, the shale is slightly 

 altered for a few inches beneath the trap, but even this is not always the case. When this 

 is compared with the intense alteration which has affected the shales beneath the Palisades, an 

 intrusive sill, for a distance of over 100 feet, the difference between the sheets is emphasized. 



Upper contacts have not been observed in many cases, but the upper surface of these 

 sheets is frequently vesicular, amygdaloidal, and scoriaceous. Locally, a thin layer of water- 

 worn trap particles, intermixed with red mud occurs between the vesicular trap and the unaltered 

 typical red shales, or the vesicules are filled with red mud. The overlying shales conform to the 

 slightly irregular, ropy surface of the trap. In frequent exposures the rolling-flow structure, 

 named by the Hawaiian Islanders pahoehoe, is visible. Nowhere have any tongues of lava been 

 found extending from the main sheet into the neighboring shales. 



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The Palisades of the Hudson, the Rocky Hill sheet north of Princeton, the Sourland 

 Mountain sheet near Lambertville, and the Cushetunk Mountain near White House are the 

 largest and most prominent of the intrusive sheets. * * * j^ addition to these, which are 

 demonstrably siUs or sheets, there are more irregularly shaped masses northwest of Pennington, 

 near Stockton, and at Point Pleasant (west of Stockton), the precise relations of which to the 

 inclosing beds are not clearly revealed. They are beyond all doubt intrusive masses, but it is 

 questionable whether they are strictly sheets. In the absence of positive knowledge as to their 

 relations with the sedimentary beds, I prefer to speak of them simply as intrusive masses. 



The evidence of the intrusive origin of all these masses, sills and others, is as follows. 

 Dikes radiate from the upper part of the sills and penetrate the overlying shales for distances 

 up to 7 miles, as measured on the surface. The sills are locally unconformable to the inclosing 

 strata, although in general they extend for long distances parallel to their strike. 



The adjacent sediments have often been greatly metamorphosed. So intense has been 

 this alteration that at distances, often of 100 feet, the rocks are as completely "baked" as those 

 immediately adjoining the trap. Measured along the surface, traces of metamorphism are 

 frequently found 1 foot from the nearest trap outcrop. The complete absence of scoriaceous 

 rock, of amygdules, of the vesicular or the rolling-flow structure is negative evidence of their 



