ISLA. GEOLOGY. 245 



blueish quartz rock with clay slate are to be observed 

 extending from Isla house to Laggan point, and onwards to 

 the borders of the Mull of Oe ; the clay slate between 

 these two latter places being much bent and contorted. 

 As the spaces occupied by these strata will be more easily 

 understood in the Map, it is unnecessary to dwell on 

 them ; the rocks, separately considered, present no par- 

 ticular interest. At the headland just mentioned, the alter- 

 nations are very conspicuous in consequence of the preci- 

 pices ; great contortions being also visible on its western 

 border, with more considerable irregularities of position 

 than in any other part of the island. The quartz rock 

 here occupies the middle place, and the schists are placed 

 on each side. The lateral continuation of these schists 

 forms that part of the island denominated the eastern 

 flat, their position becoming irregular, occasionally even 

 vertical ; while they are now and then found alternating 

 with quartz rock, both of the finer kind and of the conglo- 

 merated coarse texture. They present different varieties 

 of clay slate and micaceous schist ; both these substances 

 occurring, as in Scarba and Jura, in an order so irregular 

 that it is impossible to distinguish them in description. 

 I have in this detail purposely omitted some of the 

 schistose rocks, which occur among those already de 

 scribed, just as they have been shown to do in Jura ; on 

 account of the small spaces which they occupy and the 

 impossibility of pointing out, either in description or in 

 the Map, the places where they are situated. These are, 

 varieties of chlorite schist, of talc schist, and of horn- 

 blende schist. It is not unusual to find these substances 

 occurring in beds of micaceous schist elsewhere ; a transi- 

 tion from the latter to one or other of the former, fre- 

 quently accompanying the change. Similar transitions 

 also happen between the same substances and clay slate, 

 of which numerous examples occur on the southern border 

 of the Highlands throughout the whole line. They pre- 

 sent no particular appearances in Isla deserving of attention, 



