100 REPORT — 1861. 



— ^the Lingula "flags' oi- "zone priniordiale " of Eolioniia — ^having no representa- 

 tive in the nortli-western Highlands, there is necessarily a complete unconformity 

 between the fossil-bearing crystalline limestones and quartz-rocks with the Maclurea, 

 Murchisonia, Ophilcta, Orthis, Orthoccratites, &c., and those Cambrian rocks on 

 which they rest. 



A great revolution in the ideas of many an old geologist, including myself, has 

 thus been effected. Strengthened and confirmed as my view has been by the con- 

 cordant testimony of Ramsay, Harkness, Geikie, James, and others, I have had no 

 hesitation ia considering a very large portion of the crystalline strata of the High- 

 lands to be of the same age as some of the older fossiliferous Silurian rocks, whether 

 in the form of slates in Wales, of greywacke-schist in the southern counties of 

 Scotland, or iu the conditions of mud and sand at St. Petersburg. The conclu- 

 sion as respects the correlation of all the older rocks of Scotland has now indeed 

 been summed up by Mr. Geikie and myself in the ' Geological Sketch-Map of 

 Scotland,' which we have just published, and a copy of which is now exhibited*. 

 Not the least interesting part of that production is that which explains the age 

 of all the igneous or trappean rocks of the south of Scotland, as well as all the 

 divisions of the Carboniferous formation, and is exclusively the work of my able 

 colleague. 



But if, through the labours of hard-working geologists, we have anived at a clear 

 idea of the first recognizable traces of life and their sequences, we are yet far from 

 having satisfied our iniuds as to the modus operandi by which whole regions of such 

 deposits have, as in the Highlands, been transmuted into a crystalline slate. Let 

 us therefore hope that, ere this Meeting closes, we may receive instruction from 

 some one of the baud of foreign or British geologists who have by their experi- 

 mental researches been endeavouring to explain the processes by which such won- 

 derful changes in the former condition of sedimentary deposits have beeu brought 

 to light ; such as that by which strata once resembling the incoherent Silurian clay 

 •which we see iu Russia have been hardened into such rocks as the slaty grauwacke 

 of other regions, and how hard schists of the south of Scotland have been meta- 

 morphosed into the crystalline rocks of the Highlands. But why are British geo- 

 logists to see any difficulty in admitting what 1 have proposed, that vast breadths 

 of these crystalline stratified rocks of the Highlands are of Lower Silmian age ? 

 Many years ago I suggested, after examination, that some of the ciystalline rocks 

 near Christiania in Norway were but altered extensions of the Silmian deposits of 

 that region ; and, since then, Mr. David Forbes and M. Kjerulf have demonstrated the 

 truth of the suggestion. Again, and on a vastly larger scale, we know that in North 

 America all the noted geologists, however they may differ on certain details, agi'ee 

 in recognizing the fact that the vast eastern seaboard range of gneissic and micaceous 

 schists is made up of metamorohosed strata, superior even to the lowest of the 

 Silmian rocks. Logan, Rogers, Hall, and Steii'y Hunt are decidedly of this opinion ; 

 and the point has been most ably and clearly set before the public by the last-men- 

 tioned of these geologists f, who, being himself an accomplished chemist, has given 

 us some good illusti'ations of the probable modus operandi in the bringing about 

 of these changes. 



The importance of the inquiries to be made by chemical geologists into this 

 branch of our science was not lost upon the earlier members of the British Asso- 

 ciation. Even in the year 1833, a committee was appointed to endeavour to illus- 

 trate the phenomena of the metamorphism of rocks hy experiments carried on in 

 iron-fm-naces. After a series of trials on various mineral substances, the Rev. W. 

 Vemon Harcourt, to whom we owed so much at our foundation, has, as the reporter 

 of that committee, been enabled to present to the Association that lucid Report on 

 the actual effect of long-continued heat which is published in oiu- last volume. In 

 referring you to that document, I must, as an old practical field-geologist, express the 

 gratification I feel in seeing that my eminent friend has, in the spirit of true induc- 

 tive philosophy, arrived, after much experiment and thought, at the same conclusion 

 at which, in common with Sedgwick, Buckland, De la Beche, Phillips, and others 

 in my own coimti-y; and with L. von Buch, Elie de Beaumont, and a host of geolo- 



* This map is already on sale in Manchester, 

 t American Journal of Science, May, 1861. 



