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MUSEUM OF COMPAKATIVE ZOOLOGY. 



267 



Besides the dikes, there are sheets of trap cutting the sandstone at 

 a small angle, or perhaps in places conformable to the bedding. One 

 of these begins close to the corner of the Middle Turnpike and the 

 Cheshire road, and can be easily followed several hundred feet obliquely 

 up the slope to the northwest; it makes a little bench on the hillside, 

 rendered clearer by some quarrying work at several points ; it is about 

 fifteen feet thick, dense throughout, and its columns are closely at 

 right angles to its bounding surfaces; the sandstone is baked for a few 

 inches below it, and the only sandstone found on its back was hard- 

 ened. Another similar bench is seen a little higher; and a third makes 

 a well-formed mesa near by, locally known as Mount Tom. All of these 

 are probably ijitrusions ; but they have not the regular vertical position 

 shown in Chapin's general section (see fig. 8). The trap here is more 

 Irregularly intruded than at any other i)laco I have visited. 



There is a good exposure of sandstone on 



The strata here 



G. N'ew Haven, Conn. 



the southwestern face of West Rock imder the trap, 

 are of coarse granitic sand, and red and purple shales; sometimes firm, 

 but with several purple shaly beds; they do not show so much mcta- 

 morphism as the rpcks beneath the Talisades, but nevertheless appear 

 to be distinctly changed from their original condition for several feet 

 from the trap, thus gaining a compact crystalline texture in certain 



layc 



rs. 



The trap is fine at the base, where it is conformable to the 



sandstone, and very compact through the whole mass : no amygdaloid 

 was seen at any point on the face or back. 



The eastern slope near the southern end of the Rock is covered by 

 shaly sandstone, for a considerable distance toward the top ; it is often 

 exposed in little gullies, and shows a variety of colors from gray to 

 purple and bright brick-red. But for several hundred foct beyond the 

 uppermost exposure, no rock is seen till the firm trap appears ; at least 

 such is the case on the path leading up to the "Judges' Cave,"* and 

 along several gullies farther south. Undoubtedly a junction may be 

 found by searching farther to the north. In the covered space, several 

 fragments were found resembling baked shale; they are probably from 



nearer the junction. 



Pine and Mill Rocks are simply large dikes of compact trap, about 



vertical, cutting across nearly horizontal granitic sandstones ; a marked 

 consolidation has been produced by their heat for ten or twelve feet at 

 least from their sides. Their width and direction are variable : the 



* A rude shelter under some boulders, where ** Cromwell's Judges" were con- 

 cealed for a time. 



