PROCEEDINGS FOR 189(1 XCI 



heterogeneous, embracing Silurian, Cambrian and Archa-an. Huronian 

 and its boundaries, so far as ascertained, have been indicated on published 

 maps, but. unlike Quebec or Taconic, it has never been considered or been 

 shown b}' any Canadian geologist to do otherwise than occupy the posi- 

 tion, or fill the gap, between Laurentian and Lower (Jambrian. It does 

 so still, but its subdivisions are being gradually worked out and defined. 

 Two of these are Coutchiching and Iveewatin. But they are not systems, 

 and mean no more than do the subdivisions Trenton, Calciferous and 



Potsdam. 



" Yours sincerely, 



" Alfred R. C. Selwyn." 



Archaean volcanic rocks are now, however, no longer in the domain 

 of "fancy sketches," nor is it now held that certain Archaean rocks have 

 "no resemblance to lava or igneous ejections." and were all "once sediment- 

 ary beds." By the aid of the microscojje these old volcanic ejectamenta 

 are being recognized and descanted on from Maine to the Rockies.' And 

 I venture to predict that the same useful instrument will very shortly 

 put an end to prevailing theories of deposition respecting Archœan rocks 

 and their origin. But as my old friend and colleague, Sir A. Ramsay, 

 said, " I do not believe in looking at a mountain, with a microscope." ^ 



The purely theoretical dogma that continents have always been con- 

 tinents, and oceans have always been oceans, is to me much more like a 

 " fancy sketch ; " especially when it is admitted that they, orportions of 

 them — why not the whole ? — may have been submerged some thousands 

 of feet ; and it becomes still more fanciful when we are told that accu- 

 mulation of sediment is the cause of depression. This seems to be a com- 

 plete transposition of cause and eff'ect, and is certainly not supported by 

 anything presented by the rocks themselves or in their structure. 

 Practical experience, apart from theory, tells us that if we want to secure 

 the accumulation of materials by unaided natural causes, a depression is 

 essential, and is a precursor, not a consequence, of accumulation, and it 

 at once secures the effect. Plausible and ingenious theories are here cer- 

 tainly in conflict with actual and well known facts. 



The greatest depression of the lithosphère is that of the ocean floor. 

 It constitutes three-fifths or thereabouts of the whole surface. We know 

 but little of its hills and valleys, its plains and its rivers. " There is a- 

 river in the ocean," writes Maury; but we do know something of its 

 peaks and mountain summits ; and we find that in structure and com- 

 position they correspond very closely with those of the continents. They 

 have been built up like those on land by the internal and external agencies 

 I have spoken of as operating on the continents in destruction and con- 



1 Pre-Cambrian Volcanoes in Southern Wisconsin. Hobbs. Vol. VII., Geo. Soc. 

 of Am., 1895. 



2 Page 343, Geike's Memoirs of Sir A. C. Ramsay. 



