328 GEOLOGICAL APPEARANCES 



rocks of this substance have not a stratified structure, nor do 

 they appear to form a bed. 



67. From the nature of the place, the junction of the sieni- 

 tic greenstone with the adjoining strata cannot easily be tra- 

 ced, and the rocks of either kind present few remarkable cir- 

 cumstances. We found, however, soiiie pieces of granular 

 quartz and gneiss imbedded in the sienitic greenstone, and 

 there is an appearance of veins of sienite cutting the large mass 

 of granular quartz in the middle of the river. 



68. At the foot of the I'all, there is a vein of granular lime'- 

 stone approaching to compact dolomite, which cuts the rock 

 of sienitic greenstone for three or four feet, and varies in thick- 

 ness from an inch to less than half an inch. Its fracture is 

 splintery, but passing to the foliated. Its hardness is consider- 

 able ; and from this, as well as from the appearance of its de- 

 composed surface, it is evidently penetrated by some siliceous 

 substance. Its colour is a dark greenish-grey ; its greenish hue 

 being probably derived from chlorite. It does not graduate 

 into the sienitic gi-eenstone that forms its walls, and there are 

 small pieces of the sienitic greenstone imbedded in it. Its ter- 

 mination could not be seen in either direction. 



69. The bridge over the Tilt, rather more than half a mile 

 above Forest I^odge, stands at the place referred to by D. 

 Twenty yards above the bridge, there is a fall of the river, 

 and the arch is thrown between two of the nearest points of 

 the precipices, which extend for a short distance on both sides 

 of the deep pool below the fall. This is by far the most 

 interesting scene in the whole valley for its geological pheno- 

 mena. For a plan of it, see Plate XVIII. 



70. On the southern bank, seventy or eighty yards below 

 the bridge, is the eastern extremity of a high scar, extending 



from 



t 



