MUSEUM OF COMPARATIVE ZOOLOGY. 273 



very fine-grained. The lower ten or fifteen feet of trap is of very heavy 

 columns, two to four feet on a side, irregular or roughly rectangular ; 

 divided near the middle by rather continuous joints parallel to the sand- 

 stone bedding, sometimes breaking the rock into slabs two to ten inches 

 thick. No change of texture is seen at these joints, and some of the 

 columns ai'e continued above and below. The heavy columns suddenly 

 change upwards to smaller ones, six inches to a foot on a side, but there 

 is no corresponding change in the texture of the rock, nor is there any 

 appearance of a seam between the two parts ; it is simply a change of 

 jointing, for which I can suggest no satisfactory cause. The smaller 

 columns are not all parallel, but incline in various directions ; some 

 variation is shown in the figure where they overhang the lower columns. 

 Where thus irregular in position, they are at right angles to the present 

 surface of the ground (noted also by Cook, h, 202, 203). The same 

 change of structure is shown a third of a mile south, by Barber's Mills ; 

 again a little farther where the Delaware, Lackawanna, and Western 

 Railroad cuts a bench for its passage around the end of First Mountain, 

 here known as Garret Rock; and finally in the first and third of three 

 quarries opened on the eastern face of the mountain, over the railroad 

 station. Contacts of trap and sandstone show in all but tlie first of 

 these, but not so clearly as at the Falls ; the sandstone shows no effect 

 of heat except the slight one above described. Of these latter localities 

 the most important is that on the railroad (fig. 47), showing two strike 

 faults of small throw. The eastern and greater of the two is covered by 

 a ravine and its rubbish, but is proved by the repetition of shaly sand- 

 stone, heavy- columns, and smaller columns on either side ; from junction 

 to junction measured along the ti'ack is one hundred and sixty paces, 

 say four hundred and fifty feet ; the junction line dips with the bedding 

 10°; this gives seventy or eighty feet for the displacement, with down- 

 throw on the east. The second fault, a little farther west in the same 

 cut, is shown to be about eight feet by the displacement of the upper 

 surface of the heavy columns with downthrow to west ; the fiault is on 

 an open joint, parallel to the columns, and striking with the ridge. 



The mountain is most easily ascended by its northwest flank ; from 

 any of its higher knobs * a well-marked longitudinal valley is seen sep- 

 arating the eastern from the western summits; it extends several miles 

 with varying distinctness, and is very marked at the Notch, where the 



* Most of these knobs are well rounded by glacial action, and swie still retain 

 strife pointing directly up hill. Excellent scratches on the trap at Little Falls point 

 up into Vernon Valley between the two mountains. 



VOL. VII. —NO. 9. 18 



