102 J. W. DAWSON — SOME RECENT DISCUSSIONS IN GEOLOGY. 



may be seen to underlie the other members of our geologic column, we 

 liaA^e recently learned from Sir Archibald Geikie * that the great contro- 

 versies which have raged as to these rocks in the west highlands of Scot- 

 land ever since the order assigned to them by Murchison was called in 

 question by my friend and fellow-student, Professor Nicol, of Aberdeen, 

 has been finally settled. On comparing his arrangement with American 

 facts, and especially those displayed in the unequalled exposure of these 

 rocks in Canada, it would appear that the following correlations may be 

 stated : 



The older gneissic group of the west Highlands of Scotland does not 

 contain the whole of the Laurentian of Logan, the Lewisian of Murchison, 

 but only or mainly the lower part of it, the Ottawa group of the Canadian 

 survey. A certain limited track at Loch Maree not improbably repre- 

 sents the Upper Laurentian or Grenville series, and this certainly occurs 

 in the western islands. I use the term Upper Laurentian in the sense 

 recently given to it by Dr Adams ; f the original Upper Laurentian 

 apparently consisting, in what was regarded as its typical area, mainly 

 of igneous products. It is to be observed, however, in this connection 

 that over large areas in the west the Upper Laurentian is absent, or has 

 been removed, or is replaced by rocks of somewhat different character 

 from those of the east. 



I take this opportunity to object to the term " Archean or Basement 

 Complex " applied by some geologists to these formations. Every 

 geologic formation is complex, especially when disturbed and invaded 

 by igneous rocks, but none is more simple than the Lower Laurentian, 

 as it consists almost entirely of orthoclase gneiss ; and even the igneous 

 masses and veins have been introduced so quietly and with so little of 

 the violence of modern vulcanism that it is not easy to separate them 

 from the old beds with which they are so intimately united. I may add 

 that it seems likely that the Lower Laurentian is the oldest formation we 

 shall ever know, and that its peculiar characteristics depend on its con- 

 stituting the earliest deposits from water on the thin crust of a lately 

 incandescent globe. 



The Torridon sandstones and the associated beds of Geikie seem in 

 mineral character and in association with the Laurentian, and in the few 

 fossils which they contain, to be equivalent to the Huronian of Logan. 

 The Dalradian, at least in Ireland, would seem to be of similar character 

 and age. 



The Uriconian and Longmyndian of Geikie probably include the 

 equivalents of our Kewenian, and the same may perhaps be said of the 



* Journal of Geology, vol. 1, number 1, 1893. 

 t Journal of Geology, vol. 1, number 4, 1893. 



