FEATURES OE TRAP EXTRUSIONS IN NEW JERSEY 323 



in many places. Above the contact much of the trap is vesicular, 

 but in places dense trap comes down to the contact. The vesicular 

 trap gives on weathering a brownish, pulverulent, tuff-like material, 

 but I do not think that true tuff is present. Where not weathered it 

 contains many seams and vugs of crystals. The dense trap is some- 

 times separated quite abruptly from the vesicular form and in other 

 places there is a transition from one to the other. 



There was evidently considerable agitation here at the time of the 

 trap flow, but it does not appear to have been so violent as in the cases 

 previously described. The position of this quarry is on the eastern 

 edge of the trap sheet, somewhat removed from the line of direction of 

 the lake valley, so far as determined. I should consider that this 

 marked a spot of marshy ground in the general area of the lake basins, 

 rather than a large body of water. Professor Kemp (in a personal 

 communication) reports the discovery of reptile trails in the shales 

 underlying the trap at this quarry. 



A reference to the accompanying map will show many other 

 localities in which typical exposures have been found. In most of 

 these cases the crusted bowlders are the most prominent features 

 to be observed in the structure of the rock. In a few cases I have 

 indicated on the map outcrops of normal, dense trap. These are 

 only shown where they have some significance in defining the limits 

 of the lake area. 



FAULTS 



An explanation of the appearance of the shales beneath the trap 

 sheet at the West Paterson quarry in the midst of the trap area is 

 required. Along the eastern scarp of the ridge the sandstone series 

 is found to have everywhere a gentle westerly dip, averaging six or 

 seven degrees, as it disappears beneath the trap. Assuming that 

 this dip continued from Garret Rock westward to the quarry, 

 the base of the trap sheet should lie several hundred feet beneath 

 the surface at this point. To explain the reappearance of the 

 sandstone then we must suppose either that there has been a 

 sudden reversal in the direction of the dip or that it has been 

 brought up by faulting. There is no evidence of a reversal of dip 

 and its existence would be contrary to the general monoclinal 



