62 GEOLOGICAL FEATURES OF BUTESHIRE. 



south of this, bounded by the Eotbesay valley, consists of the two 

 upper slates, the common clay and chloritic. Subordinate to these 

 are great beds of quartz rock, the most considerable of which forms 

 the high ridge called Barone Hill. The portion extending from 

 Rothesay Valley to Kilcattan is occupied by red sandstone; and 

 finally, the southern portion, with a substratum of red sandstone, 

 consists mainly of various rocks of the trap family, erupted through 

 and overlying the sandstone. The accompanying outline of the 

 island (fig. 1) shows the relation of these strata to the valleys or 

 depressions, which are obviously a part of the system of parallel 

 fractures ranging N.E. and S.W. across Scotland, and probably due 

 to the upheaval of the mountains of the Central Highlands. 



The sandstone is in the place of the old red, as succeeding the 

 slates, and has much of the mineral character of this formation hi 

 other districts. Along the eastern shore in several places, and again 

 at Kilcattan, beds of limestone occur subordinate to it ; but unlike 

 the Arran limestones in the same subordinate positions, they have 

 no fossils containing much siliceous matter, they are of little economic 

 value, and thus have many analogies with the cornstones of the old 

 red, such as occur near the base of Ben Lomond, and in several 

 localities in Arran, the march of Achab Farm, the Fallen Rocks, 

 Glen Loig, and Kilchattan.* 



Fit;.]. 



a, Kames Bay ; L, Rothesay ; c, Kilcattan ; m, mica slate; n, clay and 

 chlorite slates ; s s, red sandstone ; t, trap ; r, the terrace. 



The dikes of Bute are composed of greenstone or basalt, and are 

 very numerous, especially on the east coast. They traverse the 

 strata in various directions, and in some cases can be traced for 

 several miles continuously, preserving nearly the same width and 

 direction throughout. The north shore of Bute is classic ground in 

 the history of the glacial beds of Scotland. It was from an exami- 

 nation of the shell beds found here that Mr Smith of Jordanhill was 

 first led to recognise the arctic character of the.se deposits. 



Arran. — The island of Arran is 20| miles long from IST.IST.W. 

 to S.S.E., 10^ miles broad, and with the Holy Isle and Piadda 

 * Professor (leikie considers all the sandstones to he newer than the old red. 



