430 



THE GEOLOGIST. 



Commencing with the oldest strata, I may now assume, from the examina- 

 tion of several associates on whose powers of observation as well as my own I 

 rely, that what I asserted at the Aberdeen meeting, in 1859, as the result of 

 several surveys, and what I first put forth at the Glasgow meeting of 1855, is 

 substantially true. The stratified gneiss of the north-west coast of the High- 

 lands, and of the large island of Lewis and the outer Hebrides, is the funda- 

 mental rock of the British Isles, and the precise equivalent of the Laurentian 

 system of Canada, as described by Sir W. Logan. The establishment of this 

 order, which is so clearly exhibited in great natural sections on the west coast 

 of Sunderland and Ross, is of great importance in giving to the science we 

 cultivate a lower datum-line than we previously possessed, as first propounded 

 by myself before the British Association in 1855. * 



Ear hitherto the order of the geological succession, even as seen in the 

 Geological Map of England and Wales or Ireland, as approved by Sir Henry 

 de la Beche and his able coadjutors, Phillips, Ramsay, Jukes, and others, 

 admits no older sediment than the Cambrian of North Wales, whether in its 

 slaty condition in Merioneth and Caernarvon, or in its more altered condition 

 in Anglesea. 



The researches in the Highlands have, however, shown that in our own 

 islands, the older palaeozoic rocks, properly so called, or those in which the 

 first traces of life have been discovered, do repose, as in the broad regions of 

 the Laurentian Mountains of Canada, upon a grand stratified crystalline foun- 

 dation, in which both limestones and iron ores occur subordinate to gneiss. In 

 Scotland, therefore, these earliest gneissic accumulations are now to be marked 

 on our maps by the Greek letter alpha, as preceding the Roman a, which had 

 been previously applied to the lowest known deposits of England, Wales, and 

 Ireland. Though we must not dogmatise and affirm that these fundamental 

 deposits were m their pristine state absolutely unfurnished with any living 

 things (for Logan and Sterry Hunt, in Canada, have suggested that there they 

 indicate traces of the former life), we may conclude, that in the highly meta- 

 morphosed condition in which they are now presented to us in North- Western 

 Britain, and associated as they are with much granitic and hornblendic matter, 

 they are for all purposes of the practical geologist " azoic rocks." The Cam- 

 brian rocks, or second stage in the ascending order as seen reposing on the 

 fundamental gneiss of the North-West of Scotland, are purple and red sand- 

 stones and conglomerates forming lofty mountains. These resemble to a great 

 •extent portions of the rocks of the same age which are so well known in the 

 Longmynd range of Shropshire, and at Harlech in North Wales, and Bray 

 Head in Ireland. 



At Bray Head they have afforded the Oldhamia, possibly an Alga, whilst at 

 the Longmynd, in Shropshire, they have yielded to the researches of Mr. Salter 

 some worm-tracks and the trace of an obscure crustacean. 



The Highland rocks of this age, as well as their equivalents, the Huronian 



* See Reports of British Association for 1855 (Glasgow Meeting). At that time 

 I was not aware that the same, order was developed on a grand scale in Canada, nor 

 do I now know when that order was there first observed by Sir W. Logan. I then 

 (1855) simply put forward the facts as exhibited on the north-west coast of Scot- 

 land ; viz., the existence of what I termed a lower or " fundamental gneiss," lying 

 far beneath other gneissose and crystalline strata, containing remains which I even 

 then suggested were of Lower Silurian age. Subsequently, in 1859, when accom- 

 panied by Professor Ramsay, I adopted at his suggestion, the word "Laurentian," 

 in comp' ; ment to my friend, Sir William Logan, who had then worked out the 

 order, and mapped it on a stupendous scale. I stated, however, at the same time, 

 that, if a British synonym was to have been taken, I should have proposed the word 

 " Lewisian," from the large island of the Lewis, almost wholly composed of this 

 gneiss. 



