■308 GEOLOGICAL APPEARANCES 



Bridge, the two extremes of the stretch were N. 38' E., and 

 N. 51° E., and the angle of dip, which was southerly, varied 

 from 26° to 38°. As far as the eye could judge, we had no 

 reason to suppose that the irregularity any where exceeded 

 these limits. 



10. Fifty yards below Gow's Bridge, the strata, which are 

 here of mica-slate, are cut by a vein of greenstone-porphyry. 

 The imbedded crystals of felspar are few and small, and the 

 base is very minutely crystallised, containing, in the place of 

 hornblende, what seems to be common actinolite ; but this dis- 

 tinction is, perhaps, of little consjequence, since Hauy has 

 been induced to unite these two substances under the same 

 species, on account of their agreement, both in the structure 

 of the crystal, and in chemical composition, as proved by the 

 analyses of Vauquelin. The vein is about ten feet thick, and 

 dips westward at a large angle. 



11. At the point A, the rocks in the bed of the river under- 

 20 a material change, and for upwards of three miles, they con- 

 sist in some places of sienite, and in others of primary strata ; 

 ^nd sometimes they exhibit masses of gneiss, granular lime- 

 stone, crranular quartz, hornblende-slate, and other materials of 

 primary strata, interspersed among unstratified masses of sie- 

 nite. An idea of the irregular succession of the stratified and 

 unstratified masses may be derived from the plan *, which in- 

 cludes the course of the river between this point and a bridge 

 above Forest Lodge. Appearances of the same kind occur for 

 a mile and a half farther up. 



12. In 



* This plan was laid down, by taking bearings with the compass along the 

 bank of the river, according to its changes of direction and by pacing the dis- 

 tances. The length of a certain number of paces was determined by measure- 

 ment. 



