Geology and Mineralogy. 353 



(Long Branch Division), and about 200 yards south of the wtation 

 at Maiirer, Middlesex Co., in a pit known as Dunnigan's pit. 

 The excavation, having proceeded at a level slightly below the rail- 

 road for some '200 feet into the hill, developed a vertical wall of 

 clay, in which was shown the faulting herein described. This 

 wall or quarry face was 150 feet long and 7 to 10 feet high, and 

 showed, as it progressed, five or six separate faults, each of which 

 slightly dislocated the layers of the deposit. 



The clays here, as elsewhere in this region, are nearly horizontal, 

 having a dip of only 35 to 60 ft. per mile toward the southeast. 

 They form part of a coastal plain deposit, on which, as the 

 prominent black lignite seam in the section shows us (see fig. 1), 

 vegetation grew for a certain period, to be overwhelmed again 

 after a time by the clay deposition. It will be noted that the 

 layers of clay immediately above and below the lignite are darker 

 in color than those farther away from it, in this case indicating a 

 larger portion of carbonaceous matter in the former. The clay 

 layer below the lignite seam shows numerous woody lignite fibers, 

 extending downward in a vertical direction. These without doubt 

 represent the roots of the earliest vegetation which furnished the 

 lignite. Seams of this kind are very uncommon in the pits of 

 Middlesex County, though isolated logs and stumps of lignite are 

 common. 



It will be noted that but for the presence of the black seam and 

 the darker clays surrounding it, there would be no well-marked 

 evidence of any faulting, because of similarity in the color and 

 texture of the beds. Even a very close scrutiny of the clay wall 

 failed to show any noticeable crevice along the fault plane which 

 subsequent pressure had not completely closed. Even the fault 

 scarp, which would normally appear at the top, was completely 

 removed by the glacial action, and the bowlder clay, which was 

 later deposited above, of course can show no evidences of the 

 faulting, of which it is entirely independent. 



The several faults exposed were all parallel in strike, which 

 was roughly N-E-S-W, at right angles to the movement of the 

 ice, Avhich is suggestive. Moreover, the downthrow, which 

 varied from four inches in the smallest one to about two feet in the 

 one here figured, was in every case toward the southeast, away 

 from the source of pressure. 



Some interesting geological speculation might be based on 

 these phenomena. For example, why did folding take place in 

 one case and faulting in another? Why are not phenomena of 

 this kind more common in those clay deposits which lie within 

 the terminal moraine ? Was the local deformation due to exces- 

 sive thickness of the ice, or to local weakness in the clay, and if 

 so, may it not have been a similar local variation in strength that 

 caused folding in one case and faulting elsewhere ? 



Mlneralogical Department, Princeton University. 



