ADDRESS. IS 



and its aspect, though more ragged and abrupt, and of greater elevatioij, 

 must have been of that character which we still see in the Lauren- 

 tian hills. The distribution of this ancient land is indicated by the 

 long lines of old Lanrentian rock e^:tending from the Labrador coast 

 and the north shore of the St. Lawrence, and along the eastern slopes of 

 the Appalachians in Ameiica, and the like rocks of the Hebrides, the 

 Western Highlands, and the Scandinavian mountains. A small but in- 

 teresting remnant is that in the Malvern Hille, so well described by HoU. 

 It will be well to note here and to fix on our minds that thes'^ ancient 

 ridges of Eastern America and Western Europe have been greatly denuded 

 and wasted since Lanrentian times, a7id that it is along their eastern 

 sides that the greatest sedimentary accumulations have been deposited. 



From this time dates the introduction of that dominance of existing 

 causes which forms the basis of uniformitarianism in geology, and which 

 had to go on with various and great modifications of detail, through the 

 successive stages of the geological history, till the land and water of the 

 northern hemisphere attained to their present complex structure. 



So soon as we have a circumpolar belt or patches of Eozoic ' land and 

 ridges running southward from it, we enter on new and more complicated 

 methods of growth of the continents and seas. Here we are indebted to 

 Le Conie for clearly pointing out that our original Eozoic tracts of con- 

 tinent were in the earliest times areas of deposition, and that the first 

 elevations of land out of the primeval ocean must have differed in import- 

 ant points from all that have succeeded them ; but they were equally 

 amenable to the ordinary laws of denudation. Portions of these oldest 

 crystalline rocks, raised out of the protecting water, were now eroded by 

 atmospheric agents, and especially by the carbonic acid, then existing 

 in th© atmosphere perhaps more abundantly than at present, under 

 whose influence the hardest of the gneissic rocks gradually decay. The 

 Arctic lands weie subjected in addition to the powerful mechanical 

 force of frost and thaw. Thus every shower of rain and every swollen 

 stream would carry into the sea the products of the waste of land, sorting 

 them into fine clays and coarser sands ; and the cold currents which cling 

 to the ocean bottom, now determined in their courses, not merely by the 

 earth's rotation, but also by the lines of folding on both sides of the 

 Atlantic, would carry south-westward, and pile up in marginal banks of 

 great thickness, the debris produced from the rapid waste of the land 

 already existing in the Arctic regions. The Atlantic, opening widely to 

 the north, and having large rivers pouring into it, was especially the 

 ocean characterised, as time advanced, by the prevalence of these pheno- 

 mena. Thus throughout the geological history it has happened that, while 

 the middle of the Atlantic has received merely organic deposits of shells 

 of Foraminifera and similar organisms, and this probably only to a small 

 amount, its margins have had piled upon them beds of detritus of immense 



' Or Archaean, or pre-Cambrian, if these terms are preferred. 



