1873.] GEIKIE GLACIAL PHENOMENA OP OUTER HEBRIDES. 539 



haps most numerous. In some places the stones are so closely 

 aggregated as to give to the deposit the appearance of a very coarse 

 angular shingle. By far the greater majority consist of gneiss ; and 

 I did not see a single stone in what (to distinguish it from certain 

 other stony clays) I have called the " bottom till," which might not 

 have been derived from the rocks of Lewis itself. At the Butt, 

 however, I detected a number of red-sandstone boulders lying loose 

 in the fields, which are most probably derived from the subjacent till, 

 and which could hardly have come from the Cambrian district near 

 Stornoway. Bed sandstone, however, may occupy the sea-bottom at 

 no great distance from Cellar Head ; and hence we are not compelled 

 to suppose that these sandstone fragments have travelled from the 

 mainland. At Barabhais, again, the sea-beach is strewn with frag- 

 ments of the same rock intermingled with boulders of gneiss. 

 These, I do not doubt, are derived from the wreck of a stony clay, 

 some portion of which is still seen along the sea-coast of that neigh- 

 bourhood. The red-sandstone fragments may quite well have come 

 from the Stornoway district, which lies to the south-east of 

 Barabhais. 



In shape, the stones and boulders of the bottom till exactly 

 resemble those of the Scottish Lowlands, and constantly show that 

 peculiar blunted form and smoothed surface which are so charac- 

 teristic of glacial work. Few, however, exhibit any striae. The 

 harder- and finer-grained rocks, it is true, are almost invariably 

 scratched ; but rocks of this kind do not abound. The comparative 

 absence of well-scratched stones, however, is quite in keeping with 

 the rarity of striated rock-surfaces. For both we have doubtless 

 to thank the lithological character of the gneiss itself. In further 

 proof of this I may remark that the fragments of granite and 

 gneiss that occasionally occur in the till of the Scottish Lowlands, 

 even so far south as the valley of the Irvine, seldom or never show 

 striae, although they are otherwise well glaciated. 



The Lewisian till is quite unstratified. Many hundred sections 

 were examined ; and only in one instance did any thing like strati- 

 fication present itself. This was in a cutting made for a stream that 

 issues from Loch Airidh an Eipe, four miles west from Stornoway. 

 The section showed a deposit of the usual unstratified till, with a 

 number of striated stones, and two distinct lines of boulders, some 

 five or six feet apart. I may also add that at several points along 

 the south-east coast of the peninsula of Eye a bed of gravel and 

 rolled stones comes between the till and the subjacent gneiss. 



It is impossible to say what depth of this bottom till there may 

 be in Lewis ; but as a rule it does not seem to exceed a few feet. In 

 stream-sections and quarry-holes it varied in thickness from 5 or 7 

 to 12 feet, but occasionally it reached as much as 15 or 20 feet. 

 Underneath the deep covering of peat which hides so much of the 

 flat and gently undulating low grounds, its thickness may 'be con- 

 siderably more. 



A close search for fossils failed to detect the slightest trace of any 

 thing organic. 



