334 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Feb. 26, 



south-east corner of the island opposite to Scarpa, in the geology of 

 which this sandstone figures so prominently. The Torridon Sand- 

 stone thus forms a basin whose south-west edge is depressed or 

 broken off; and in this basin the Secondary beds have been 

 deposited in a sea prolific of life, the deposits being accumulated to 

 a maximum thickness of at least 1200 feet. . They were broken 

 through and overlain by igneous matter, which now appears in 

 most parts of the island as grey felsite (felspar porphyry) and in a 

 few places as the ordinary trap-rock, chiefly basalt or dolerite. 

 These two rocks are seen in close proximity in only one place we 

 know of, a small bay near the middle of the west coast, formed by 

 the wearing action of the waves upon a basaltic dyke. The dyke 

 appears at the head of the little bay; on the south side is the 

 common trap-rock, on the north the felsite, which continues hence 

 to occupy the coast, and extends over the whole of the western 

 slopes to the central axis of the island, and stretches southwards 

 to the south end of the island. Both rocks alike are seen to cut 

 through in dykes, to overlie, and to alter, in both situations, the 

 sedimentary deposits. A good example of both effects in the case of 

 the felsite may be seen on the east side of the bay on which Baasay 

 House is situated *. 



The northern part of the island, north of Brochel Castle, and Bona a 

 continuation of it, are composed of hornblendic gneiss, precisely the 

 same in all its characters as that of the Long Island, and of the 

 mainland of Boss and Sutherland, save that mica is always present. 

 The lowest conglomerate bed of the Torridon sandstone is seen 

 in fine section in a cliff north-west of Brochel Castle ; and the rock 

 south-east of the castle, on the shore, regarded as very peculiar by 

 M'Culloch, who describes its structure most accurately, is but the 

 lowest dark slaty unconglomerated part of the Torridon sandstone. 

 The strata dip under the sandstone of the high cliff to the south. 

 It struck me as remarkable that the fragments in the conglomerate 

 of the Castle rock are all of quartz and Torridon sandstone ; not a 

 fragment could be detected either of the adjoining gneiss or of gra- 

 nite — as if the gneiss had not been exposed to disintegration when the 

 conglomerate was forming. The map and sections (PI. XI.) will show 

 the distribution of the rocks of Eaasay ; and reference may be made to 

 Dr. M'Culloch's description (vol. i. p. 239 et seq.) of the mineral 

 structure of the rocks, and his account of their distribution, which is 

 generally very correct. Our business here is chiefly with the fossili- 

 ferous beds, of which his account is most unsatisfactory. No section 

 is given ; and not one of the fossils is named by him, though the 

 names of a few genera are suggested as those to which the speci- 

 mens may possibly belong. The only fossils known to us as having 

 been found in Baasay, before the collection now submitted to the 

 Society was made, are those given by Sir B. Murchison, p. 367 of 



* The kind hospitality of the late lamented proprietor of the Eaasay estate, 

 G. H. Eainey, Esq., and that of the present proprietor, G. Grant Mackay, 

 Esq., enabled ns to examine the island in a short time and with much ease and 

 comfort. 



