ADDRESS. 1 7 



and its aspect, though more rugged and abrupt, and of greater elevation, 

 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 Laurentian rock extending from the Labrador coast 

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

 the Appalachians in America, 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 Hills, so well described by HoU. 

 It will be well to note here and to fix on our minds that these ancient 

 ridges of Eastern America and Western Europe have been greatly denuded 

 and wasted since Laurentian times, and 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 i land and 

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

 methods of growth of the continents and seas, depending on the new 

 conditions established by the elevation of the earliest continents and the 

 consequent determination of ocean currents and of sedimentation along 

 the continental margins. Portions of the oldest crystalline rocks, raised 

 out of the protecting water, were now eroded by atmospheric agents, 

 and especially by the carbonic acid, then existing in the atmosphere 

 perhaps more abundantly than at present, under whose influence 

 the hardest of the gneissic rocks gradually decay. The Arctic lands 

 were 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 Eoraminifera and similar organisms, and this probably only to a small 

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

 thickness. Professor Hall, of Albany, was the first geologist who pointed 

 out the vast cosmic importance of these deposits, and that the mountains. 



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

 1886. ■ _ 



