GEOLOGY OF BUTE. 325 



off in several filaments, which unite again portions of 

 the rock traversed are often found entangled in the dike; 

 and these, as well as the contiguous strata, present the usual 

 metamorphic effects recognized as due to igneous action, be- 

 sides others of a peculiar and exceptional character, to which 

 we shall presently allude. 



A dike seventy feet wide emerges from the sea at the 

 mineral well near Bogany Point, and ranging nearly west 

 is seen in Huntly Place, where it has been largely quarried; 

 interrupted by the. bay, it rises again, is conspicuous across 

 the high grounds west of the town, and, crossing the island, 

 enters the sea at Ettrick Bay. Here another dike, two or 

 three times the width, enters near it, crossing from Ascog, 

 and visible in several eminences in the interior. The Rothe- 

 say mineral water, which has acquired some reputation for 

 efficacy in rheumatic, cutaneous, and glandular complaints, 

 rises in the former of these two dikes at Bogany Point. The 

 gallon of 277*274 cub. inches contains, according to the 

 analysis of the late Dr. Thomas Thomson, Professor of 

 Chemistry in Glasgow University, Com. salt, 1860*73 

 grains ; sulph. lime, 125-20 ; sulph. soda, 129-77 ; mur. 

 magnesia, 32-80; silica, 14-39: sulphuretted hydrogen, 17-4 

 cub. inches. Both dikes and this mineral water are noticed 

 at some length in "Wilson's Guide to Rothesay and the Island 

 of Bute, an excellent and neatly illustrated little work. 



The Kilchattan limestone is altered in a remarkable manner 

 by a large dike, crossing it nearly in the direction of the dip, 

 and the effects are well seen at the eastern side of the quarry. 

 Along the plane of contact with the dike the limestone is 

 altered to the state of a granular saccharine marble, which 

 on the application of a slight pressure crumbles into a fine 

 powder. This is succeeded by a hard crystalline marble, the 

 crystals appearing in distinct flakes. Between this and the 

 first change, which is one of simple induration, there are 

 many gradations. Similar effects are common at the con- 

 tact of limestone with plutonic rocks ; in some localities they 



