GEOLOGY OF THE OUTER HEBRIDES. 561 



rocks may be found, as the derivative source of the com- 

 ponents of the Conglomerates of Torridon. 



The main conclusion here is, that the Torridon Con- 

 glomerates are not, as a whole, made up of fragments 01 

 the Archaean rocks on which they rest. Murchison's des- 

 cription of the origin of the Torridon formation is wholly 

 true, however, of the Lewis Conglomerates ; and on that 

 ground alone it is a legitimate inference that the Lewis 

 and Torridon Conglomerates have had neither a com- 

 munity of origin nor a contemporaneity of formation. 



The main deposit lies on the east of Lewis, and covers an 

 area of about twenty square miles. A glance at the map 

 of the island shows the east coast, southwards from Storno- 

 way to Harris, deeply indented by sea-lochs. The peculiar 

 character of the Archaean rock in this region doubtless 

 determined this indentation. Here the gneiss is seen pass- 

 ing into soft and fissile argillaceous schists. Sometimes the 

 one predominates, sometimes the other. The high cliffs 

 formed by this compound structure, especially in the Lochs 

 district, are very much contorted and broken into arches 

 formed by the crossing and recrossing of dip joints. Weather 

 and marine agency have thus admirable conditions for their 

 destructive action on this line of coast. The shores of the 

 more sheltered sea-lochs in the district of Park, for instance, 

 at present show an example of littoral deposit which may 

 be paralleled with that which forms the coarse littoral 

 deposit at Stornoway forming the Conglomerate in ques- 

 tion. This Conglomerate lies within a rough right-angled 

 triangular area, having its basal line of four miles from the 

 neck of Arnish to a point (Bostadh) near Chicken Head, 

 the line running due east from Arnish. From this latter 

 point at Chicken Head the line runs for ten miles due north 

 to a point a short distance east of Gress across the Broad 

 Bay, and from thence the western line sweeps outwards 

 with a gentle curve to Lewis Castle in the neighbourhood 

 of Stornoway. This town is built on a cap of clay (boulder) 

 and gravel covering the Conglomerate. The fine natural 

 harbour of Stornoway has been formed by denudation of 



