384 ARRAN. GEOLOGY. SECONDARY STRATA. 



section caused by a torrent, or other fractures sufficiently 

 deep, have exposed the rocks. To detail these places 

 is impossible, as no mode of reference exists, but it is 

 every where plain that it forms at least the principal 

 and lowermost portion of the land, and that it is irre- 

 gularly covered by the rocks to which I have already 

 more than once alluded. On the shores it is more 

 exposed, and the nature of its connexions with these 

 latest rocks, may here be studied to advantage. Near 

 Blackwater bay, the interruptions thus caused are 

 frequent and very interesting, as they also are at the 

 Bennan head, and at Kildonan castle. Near Coryravie, 

 where trap veins abound, the strata are much confused 

 and mixed with shale. Within land, the course of the 

 Sliddery presents the most conspicuous and extensive 

 portion in this quarter, and here it is abundantly inter- 

 stratified with shale. 



A peculiar circumstance occurs in the sandstone at 

 the places where it joins the masses of claystone or 

 porphyry which so often interfere with it. Within a 

 few inches of these junctions, it acquires a more indu- 

 rated texture, and when broken and held so as to reflect 

 the light, a section or fracture of a quartz crystal may 

 be perceived. This appearance is analogous to that 

 which occurs in augit rock, and it may perhaps be 

 supposed to have resulted from the action of the 

 neighbouring vein. It occurs also in similar situations 

 in Lamlash island. 



There is not much more of the sandstone to be 

 found requiring description. Between Drumodune and 

 Tormore, both the red and white kinds occur in hori- 

 zontal beds, and they are here very much intersected 

 by veins of pitchstone, porphyry, and trap, and inter- 

 mingled with masses of some of these substances. Be- 

 tween the Machrie and the lorsa, the red sandstone 

 is again seen extending for some little way up the 

 course of that river; the beds being here in an 



