434 
THE GEOLOGIST. 
has thus been effected. Strengthened and confirmed as my view has been by 
the concordant testimony of ILamsay, 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 ojierandi 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 tliat 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 difl&culty 
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 1 hat 
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 difier 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, j who, being him- 
self an accomplished chemist, has given us some good illustrations of the pro- 
bable modus operaiidi 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. Yernon 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 efl'ect of long-continued heat which is pub- 
lished in our last voluuie. In referring you to that document, I must, as aa 
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, Buckland, De la Beche, Phillips, and others in my own country, 
* This map is already on sale in Manchester, 
t " American Journal of Science, " May, 1861. > 
