Kjeological Address at Manchester. 407 



fhe Highlands to be of the same age as some of the older fossili- 

 ferous Silurian rocks, whether in the form of slates in Wales, 

 of grauwacke-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 interest- 

 ing part of that production, 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, is exclusively the 

 work of ray able colleague. 



" But if, through the labours 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 deposits have, as in the Highlands, been transmuted into a 

 crystalline state. 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 re- 

 searches been endeavouring to explain the processes by which such 

 wonderful changes in the former condition of the sedimentary de- 

 posits have been brought to light ; such as that by which strata 

 once resembling the incoherent Silurian clay which we see in 

 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 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 stra- 

 tified rocks of the Highlands are of Lower Silurian age ? Many 

 years ago I suggested, after examination, that some of the crystalline 

 rocks near Christiana iu 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 sug- 

 gestion. Again, and on a vastly larger scale, we know that in 

 North America all the noted geologists, however they may difl"er 

 on certain details, agree in recognising the fact that the vast east- 

 ern seaboard range of gneissic and micaceous schists is made up 

 of metamorphosed strata, superior even to the lowest of the Si- 

 lurian rocks. Logan, Rogers, Hall and Sterry Hunt are decidedly 



