S20 GEOLOGICAL APPEARANCES 



40. At the lower end of the chasm, the rock is a large bed of 

 gi-anular quartz, stretching across the river in the diieciion of 

 about N. 56 E. Its stretch is indicated in the plan * of A 

 (Plate XV I.) by a line expressing the water-line upon its 

 southerly face, and referred to by the figure 1. Its dip is to 

 the south-east, at an angle of about 45 . Its structure is not 

 stratified. 



41. Immediately below this, (at 2 in the plan) there appears 

 a rock consisting of quartz, penetrated by compact dolomite. 

 Little of it is visible on the southern bank, but what there is, 

 agrees in its general character with the larger masses on the 

 northern, and there is probably a bed of it, conformable to that 

 of granular quartz. The masses of it on the northern bank, 

 are intermixed with others of granular quartz, but we could 

 not pronounce them to be in alternating beds. 



42. The rock on the north side is then concealed by the soil 

 for a considerable distance down the river, except that, about 

 forty yards below the quartz rock, (at 3 in the plan), there may 

 be seen in the channel some small masses of gneiss, interstra^ 

 tified with, and graduating into, mica-slate. The stretch of 

 these strata is N. 63" E., and their dip to the south-east, at an 

 ano-le of about 45'. Some of the gneiss is so highly crystalli- 

 sed, as to have entirely lost its stratified structure, and is here 

 and there in the form of veins, one or two inches in breadth, 

 and cutting the strata of mica-slate at a very small angle. Fi- 

 gure I, in Plate XIX, is a sketch of a horizontal section of a 

 forked vein of this kind. 



43. On the southern bank, the strata are much covered by 

 soil for a short distance below the quartz rock, but granular 



limestone 



* In this plan the rocks were merely sketched in by the eye. So likewise in 

 •;he plan of D, 



