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Progress of Geology. 9 
firmed 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 graywacke-schist in the southern counties of Scot- 
land, 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 Scot- 
Jand, as well as all the divisions of the Carboniferous formation, 
and is exclusively the work of my able colleague. 
But if through the labors of hard-working geologists, we have 
arrived at a clear idea of the first recognizable 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 depos- 
ites have, as in the Highlands, been transmuted into a erystal- 
line slate. Let us therefore hope that, ere this meeting closes, 
we may receive instructions from some one of the band of for- 
* This map is already on sale in Manchester. 
Am. Jour. Sc1.—Seconp Series, VoL. XXXII, No. 97,—Jan., 1862. 
7. 
