96 



PROF. T. G. BONNET S PETROLOGICAL NOTES ON THE 



places the " quartzite " series crosses for a short space over to this 

 left bank of the former valley. 



We have thus a very irregular slip of Hebridean gneiss, capped in 

 part by some Torridon Sandstone, bounded by two or more faults, 

 which bring down the quartzite and calcareous series on the one hand 

 and the newer gneiss series on the other (figs. 2 & 3)*. 



In the section given by Sir E,. Murchison (Q,. J. G. S. vol. xvii. 

 p. 191) a small patch of " syenite" is also marked as occurring on 

 the right bank of Loch Maree, near its head. Of the gneissose 

 character of this I have not any doubt ; but I also found there a 

 rock which, both macroscopically and microscopically, appears to be 

 a true diorite. I saw no signs of intrusion, and think the presence 

 of this patch of the older rock may be explained by faulting, though 

 I am not prepared at present to say in what manner that is to be 

 connected with the other faults. 



Fig. 2. — Section in Glen Laggan along the line A in fig. 1. 



Fault. Fault. 



Fig. 3. — Section in Glen Laggan along the line B in fig. 1. 



Fault. 



(2) Hebridean Gneiss, together with the so-called Syenite. 

 The macroscopic characters of this rock in the present district 

 have been already described by previous observers, so it wiU suffice 

 to make a few remarks on the microscopic structure of the specimens 

 which^ I collected. These were obtained from the above-named 

 localities m Glen Laggan, at intervals on the right bank of Loch 



.* } ^^ad with me a copy of Dr. Hicts's section (vol. xxnv. p. 814), but entirely 

 tailed to reconcile it with what I saw on the ground. 



