THE GEOLOGIST. 



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

 the concordant testimony of Ramsay, Harkness, Geikie, James, and others, I 

 have had no hesitation in considering a very large portion of the crystalline 

 strata of the Highlands 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 in the conditions of mud and sand at St. 

 Petersburg. The conclusions as respects the correlation of all the older rocks 

 of Scotland have 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 arrived at a 

 clear idea of the first recognisable traces of life and their sequences, we are 

 yet far from having satisfied our minds 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 instructions from some one of the band of foreign or British geologists 

 who have by their experimental researches been endeavouring to explain the 

 processes by which such wonderful changes in the former condition of sedi- 

 mentary deposits have been brought to light, such as that by which strata once 

 resembling the incoherent Silurian clay which we see in Russia, has been 

 hardened into such rocks as the slaty grauwacke of other regions, and how hard 

 schists of the south of Scotland have been metamorphosed into the crystalline 

 rocks of the Highlands. But why are British geologists to see any difficulty 

 in admitting what I have proposed, that vast breadths of these crystalline 

 stratified rocks of the Highlands are of Lower Silurian age ? Many years ago 

 I suggested, after examination, that some of the crystalline rocks near Chris- 

 tiana in Norway were but altered extensions of the Silurian 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, agree in recognising that the vast eastern seaboard range of gneissic 

 and micaceous schists is made up of metamorphosed strata, superior even to 

 the lowest of the Silurian rocks. Logan, Rogers, Hall, and Sterry Hunt are 

 decidedly of this opinion ; and the point has been most ably and clearly set 

 before the public by the last-mentioned of these geologists,f who, being him- 

 self an accomplished chemist, has given us some good illustrations of the pro- 

 bable 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 

 Association. Even in the year 1833, a committee was appointed to endeavour 

 to illustrate the phenomena of the metamorphism of rocks by experiments car- 

 ried on in iron-furnaces. After a series of trials on various mineral substances, 

 the Rev. W. Vernon Harcourt, to whom we owed so much at our foundation, 

 has, as the reporter of that committee, been enabled to present to the Associa- 

 tion that lucid report on the actual effect of long-continued heat which is pub- 

 lished in our 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 inductive philosophy, arrived, after 

 much experiment and thought, at the same conclusion at which, in common 

 with Sedgwick, Bucklaud, De la Beche, Phillips, and others in my own country, 



* This map is already on sale in Manchester, 

 f "American Journal of Science," May, 1861. 



