MULL. GEOLOGY. 555 



formerly made on this subject, to enter into more minute 

 details respecting its mineral structure. Geologists will pro- 

 bably consider the whole series as appertaining to gneiss. 



A long and interesting line of the junction of these 

 rocks with the granite, can be traced at Loch Laigh, 

 the shore fortunately lying in a direction oblique to the 

 line of junction. It presents a very distinct view of 

 appearances of considerable value towards the history of 

 granite, which, however frequent in the mainland of Scot- 

 land, are no where within my observation to be seen with 

 equal ease, and with equal freedom from doubts respecting 

 their nature. In some places the junction takes place 

 between the granite and the micaceous schist, in others 

 between the former and the quartz rock. This is an 

 important circumstance, since, these beds being parallel, 

 the granite is not parallel to them, being sometimes 

 found in contact with the one, and sometimes with the 

 other. It occupies therefore a position which may be 

 represented by the subjoined design.* In the rocks which 

 can be proved to follow each other in a conformable 

 and stratified manner, the flat surface of any one stratum 

 is every where in contact with that of the next, and by this 

 character they are known to have regularly succeeded each 

 other from the bottom upwards, even when no other proofs 

 of this are present. Here, there is no such consecutive 

 order, the quartz rock which is in contact with the granite 

 in one place being removed from it by interposed beds 

 of micaceous schist in another : an appearance which we 

 should not expect had these rocks been deposited in 

 succession on an uneven basis. This circumstance occurs 

 in other situations in similar cases, and presents an argu- 

 ment in favour of the posteriority of granite to the strati- 

 fied rocks under which it lies. 



In some parts of this junction the stratified rocks lie in 

 contact with the granite without much loss of their ori- 



* Plate XX. fig. 8. 



