﻿1861.] 



MOTtCHISON AND GEIKIE HIGHLANDS. 



195 



below another Cambrian crag, above which comes a snowy cliff of 

 quartz-rock, forming the summit of the mountain. 



The Cambrian rocks support hardly any vegetation, the quartz- 

 Fig. 11. — Enlarged Section of the Point marked * in Fig. 10. 



b. Cambrian sandstone and conglomerate. c. Quartz-rock. 



rock still less. There is, therefore, no obscuration of the lines of 

 junction, save such as arises from the debris of the crags, worn down 

 as these are by the rains and frosts of winter, that tell especially 

 upon the quartz, splitting up its beds and covering its surface with 

 piles of loose, rough, angular blocks, on which it is often perilous 

 to tread. There is no difficulty in determining which are lines of 

 fracture and which lines of regular superposition : the section, indeed, 

 is nearly as distinct as it can be drawn on paper. The uppermost 

 ledge of red sandstone dips E. 4° to 10° S., at 30° to 36° ; the 

 quartz-rock which covers it dips E. 4° to 10° S., at 35° to 42°. 

 These figures are given as the mean of several observations made at 

 intervals along the exposed ledges. They show that, in a general 

 sense, the two series of deposits are conformable ; and this conformity, 

 could we obtain unweathered surfaces for careful measurements, might 

 be shown to be complete. It is sufficiently evident, however, that 

 this undisturbed sequence is accidental, and that the Cambrian beds 

 had undergone erosion previous to the deposition of the overlying 

 deposits. In no instance is there anything like a passage of the one 

 series into the other ; on the contrary, everywhere along the junction 

 the line of demarcation is sharp and defined. Such sections as that 

 given in the annexed figure (fig. 12), are not uncommon where a 



Fig. 12. — Section slioiving the Junction of the Quartz-rock and the 

 Cambrian Sandstone on Scuir Dhu. 



b. Cambrian sandstone and conglomerate. c. Quartz-rock. 



bed of red sandstone has been at one point eroded, and is there un- 

 conformably overlapped by the quartz-rock. 



