1866.] J. GEIKIE— CAEEICK, AYESHIRE. 525 



attrition by water. But how they had come to be imbedded in the 

 angular breccia, and what the origin of that breccia could be, there 

 was no evidence in the hill to show. An examination of the coast- 

 section, however, was more successful. Near Bennane Head the 

 high road skirting the sea overlooks a large mass of Knockdolian 

 rock. The shape of the stones hereabouts generally approaches to 

 roundness, but they are often of very irregular form. Water- worn 

 stones, some of them six inches across, are here not uncommonly 

 intermingled with the angular and subangular fragments of which 

 the great bulk of the rock consists. Some of these rounded stones 

 show only a partially water-worn surface, the other portions being 

 roughened and subangular. Such water-worn stones increase in 

 number until we find them, in one place, forming a rude band, the 

 direction of which corresponds with the strike of a little area of 

 unaltered stratified wacke, which is here completely surrounded by 

 amorphous Knockdolian-rock. It is noteworthy that the smoothest 

 and more perfectly rounded stones are those composed of the hardest 

 and most compact rock ; whUe those which have lost their smoothed 

 surfaces consist of less hard and compact rock and are very gene- 

 rally amygdaloidal, the vesicles being of the usual spherical shape. 

 We are therefore justified in concluding that the brecciiform rocks 

 under review have resulted from the alteration of beds of conglome- 

 rate. The stones often look as if they had been squeezed while in 

 a softened condition. I have picked out two water- worn stones, 

 which appeared to have been flattened against each other ; and some- 

 times a somewhat rounded amygdaloidal stone would be found with 

 with a harder pebble partially squeezed into it, and strongly adhe- 

 ring. A few stones, all much of a size, seemed as if they had been 

 pressed together while in a softened state, and had thus assumed 

 regular hexagonal forms. 



There are several other points of interest in connexion with these 

 brecciiform masses, especially as regards their relations to the green 

 paste-rock; but their consideration at present would involve too 

 much detail. In places where the original condition of the beds 

 has been closer-grained or finely comminuted, we may have areas 

 somewhat analogous to the pseudo-bombs of nascent amygdaloid : 

 these, by their union, go to form a compact felstone. 



The coarser parts of Knockdolian rock also shade off into a simi- 

 lar hard compact shattered felstone — a result brought about by the 

 welding or soldering together of the angular brecciiform frag- 

 ments*. 



D. Finely Orystalline Felstones. 



A large jii'oportion of the felspathic metamorphic rocks consists 

 of finely crystalline and compact felstone. These rocks are well 

 exposed at various points along the coast to the north of Bennane 

 Head, but they are better seen upon the whole in the interior of the 

 country, along hill-sides and in stream-sections. They seldom show 



^ Conglomerates in various stages of alteration have been examined in other 

 localities of the district, and will be described in the Memoir of the Geological 

 Survey to accompany the Map, sheet 7. 



