Vol. 59.] TORRIDONIAN, ETC. OF THE ISLE OF RUM. 195 



exceed a few feet in thickness, and it is not continuous every- 

 where. It is best seen on the eastern side of the area. Along the 

 southern border it is in most places wanting, though lenticles 

 of limestone are found at intervals at the base of the overthrnst 

 rocks. 



To this basement-band succeeds a much greater thickness of crush- 

 breccia, which we may estimate at 100 to 150 feet. The material 

 is red sandstone, only occasionally bleached. Limestone-fragments 

 occur, but in very small proportion, though there are some larger 

 lenticles of that rock, especially towards the base. The accumula- 

 tion is more properly a crush-conglomerate than a breccia, for most 

 of the sandstone-fragments are more or less rounded, and many of 

 them have the shape of rolled pebbles. There is a certain amount 

 of finer material forming a matrix, and doubtless derived from the 

 grinding down of the angles of the fragments. 



It may be remarked, in passing, that the breccia or conglomerate 

 is in two places traversed by vertical crush-bands, partly impreg- 

 nated with basalt in the fashion described in the preceding section 

 (p. 192). This lends support to the supposition that these vertical 

 crush-bands are quite distinct from the main system of disturbances, 

 and are probably of Tertiary date. The bands have the same 

 general direction as the neighbouring basalt-dykes. 



Above the crush-conglomerate, and rather sharply marked off from 

 it, is a rock which gives evidence of crushing of a more advanced 

 kind, and may be termed a mylonite. As a consequence of 

 the present eroded form of the land-surface, it is preserved only 

 in the north-western half of the area, and the crush-conglomerate 

 emerges again from beneath it along the coast-line. The thickness 

 thus remaining is about 70 or 80 feet. The rock is of a dull 

 brownish colour, and has a highly-schistose structure, breaking in 

 the manner of a shale. It consists essentially of sandstone ground 

 down and rolled out as if it had passed through a mill, as aptly ex- 

 pressed by Prof. Lapworth's term ' mylonite.' The fissile character 

 is connected with the presence of new-formed mica. There is not 

 much calcareous matter in the body of the mylonite, but small lumps 

 of limestone are sometimes enclosed, usually indicated by cavities 

 from which the carbonate has been removed in solution. There are 

 also a few large lenticles of the kind noticed lower down in the 

 section. It is remarkable that the limestone has resisted crushing 

 down much more effectually than the sandstone. 



As a minor point of interest it may be noted that, both here and 

 in the brecciated rocks below, the fragments of Durness Limestone 

 have not suffered the dolomitization which has affected so large a 

 portion of that group in districts where it occurs in place. The 

 pebbles of the same limestone in the Triassic conglomerates of Skye, 

 Eaasay, and Scalpay are also non-dolomitic. 



The occurrence of this area of highly-disturbed rocks as an 

 isolated outlier seems to preclude any direct examination of its 

 tectonic relations, as connected with the system of crust-movements 



