JURA. GEOLOGY. 211 



quent as to render it impossible to point out a place where 

 the former becomes absolutely excluded. Although the 

 eastern shore of Jura may thus be said to be formed 

 of schists, there is still a diversity in this respect in 

 the characters of the northern and southern portions. 

 From the Coryvrechan towards Lowlandrnan's bay, the 

 appearances resemble so precisely those on the east side 

 of Scarba, that it would be superfluous to describe them ; 

 the chief alternations being those of clay slate with 

 micaceous schist, quartz rock, and graywacke. In pro- 

 ceeding from Lagg ferry towards the south, the clay 

 slate diminishes in quantity, yet is never excluded ; as 

 it is found even at the southern extremity of the island. 

 But at the bay of the Small isles, the other schists 

 begin to predominate, and further to the southwards 

 the micaceous passes into chlorite schist and into a 

 sort of talcaeeous schist; these different substances 

 occupying in a great measure the whole tract on ithe 

 southern shore, from ti point near Ardfin to the south- 

 eastern angle of the island. The transition of the quarts 

 rock into the micaceous schist and into the graywacke 

 can be often traced ; as may that of the micaceous into 

 the chlorite schist; but the former of these may be 

 considered the predominant substance in the south- 

 eastern-angle of the island. I may add that the somewhat 

 rare variety of clay slate known by the name of drawing 

 slate, or black chalk, is also found in this part of Jura. 

 The mineral characters of these substances offer no 

 peculiar features. The clay slate is of the most ordinary 

 aspect, dark blue and fine, sometimes fissile and yielding 

 roofing slate. The micaceous schist ^t times contains 

 quartz, while in other cases it consists almost entirely 

 of mica. The graywacke possesses a much greater 

 variety of aspect, since it presents every transition from 

 a coarse conglomerate to a fine schist ; passing at length 

 into those varieties in which clay predominates, almost 

 to the exclusion t}f the qirarta nd mica. -Quartz veins 



