108 Mineralogy and Geology of the White Mountaifis. 



Trap Dikes at the falls in Campion. 



Two miles north of Plymouth, at the falls of the Pemigewas- 

 set, are some remarkable dikes. The whole bed of the stream is 

 of solid rock, and the river which makes here a considerable fall, 

 runs in several channels, separated by rugged rocks, each of which 

 must be crossed by a dam to secure the whole power of the 

 stream for manufacturing purposes, which is now in process of 

 execution. 



The rock is granitoid, partaking in different parts of the varied 

 character that belongs to the several members of this family, and 

 perhaps may be called gneiss, as nearly as any specific name will 

 apply ; course N. E. ; estimated dip 30^ east. This is, however, 

 quite variable, as at dike No. 6, the dip of the strata is near 60°, 

 and the cause is apparent. There is a group of dikes half a mile 

 or more above these falls, which I had no opportunity of examin- 

 ing, but hope the next season to visit them. My description at 

 present is only of that group that occurs at the falls. The num- 

 ber of dikes in this is seimi, all of which may be examined very 

 conveniently, unless it be No. 7, which, at certain heights of the 

 water, is not quite as accessible as the others. The west bank 

 is intersected by all these, which in some cases may be seen cut- 

 ting the bed of the stream, the rocky island, and even the oppo- 

 site bank ; and all occur within a distance of a quarter of a mile.* 



No. 1. Just above the bridge ; dark gray, and nearly black ; 

 contains crystals of black hornblende and points of feldspar ; crys- 

 tals and films of iron pyrites in trap and associated rock, in small 

 fissures extending from one to the other; some specimens fire 

 with steel. Course E. and W., and cuts, as in Fig. 3, the island 

 in the stream, and is seen in the eastern bank ; intersects veins 

 of quartz. 



No. 2. (First below the bridge;) direction E. and W., and in 

 upper part four feet wide ; divides a few feet from the water into 

 two branches ; the upper one is seen in the island ; structure very 

 compact, like feldspar ; fracture uneven ; color light greenish gray ; 

 powder almost a clear white ; weathered surface dark brown ; 

 fires with steel ; translucent on the edges ; effervesces abundantly 

 (in powder) with dilate sulphuric, hydrochloric and nitric acids; 



^ The accompanying sketch is not intended as a corrGct topographical vieio of 

 the falls at Carapton, but only as showing the manner in which the dikes occur. 

 The sketch was made wholly from memory. 



