94 THE CANADIAN NATURALIST. [April 



been studied by Giimbel and Crejci, who divided them into an 

 older reddish gneiss and a newer grey gneiss. But, on the Dan- 

 ube, the mass which is furthest removed from the Silurian rocks 

 being a grey gneiss, Giimbel and Crejci account for its presence by 

 an inverted fold in the strata ; while Sir Koderick places this at the 

 base, and regards the whole as a single series, in the normal funda- 

 mental position of the Laurentian of Scotland and of Canada. Con- 

 sidering the colossal thickness given to the series (90,000 feet), it 

 remains to be seen whether it may not include both the Lower and 

 Upper Laurentian, and possibly, in addition, the Huronian. 



This third Canadian group (the Huronian) has been shown by 

 my colleague, Mr. Murray, to be about 18,000 feet thick, and to 

 consist chiefly of quartzites, slate-conglomerates, diorites, and lime- 

 stones. The horizontal strata which form the base of the Lower 

 Silurian in western Canada, rest upon the upturned edges of the 

 Huronian series ; which, in its turn, unconformably overlies the 

 Lower Laurentian. The Huronian is believed to be more recent 

 than the Upper Laurentian series, although the tw r o formations 

 have never yet been seen in contact. 



The united thickness of these three great series may possibly far 

 surpass that of all the succeeding rocks from the base of the Palseo- 

 zoic series to the present time. We are thus carried back to a 

 period so far remote, that the appearance of the so-called Prim- 

 ordial fauna may by some be considered a comparatively modern 

 event. We, however, find that, even during the Laurentian period, 

 the same chemical and mechanical processes which have ever since 

 been at work disintegrating and reconstructing the earth's crust 

 were in operation as now. In the conglomerates of the Huronian 

 series there are enclosed boulders derived from the Laurentian, 

 which seem to show that the parent rock was altered to its present 

 crystalline condition before the deposit of the newer formation ; 

 while interstratified with the Laurentian limestones there are beds 

 of conglomerate, the pebbles of which are themselves rolled frag- 

 ments of a still older laminated sand-rock, and the formation of 

 these beds leads us still further into the past. 



In both the Upper and Lower Laurentian series there are seve- 

 ral zones of limestone, each of sufficient volume to constitute an 

 independent formation. Of these calcareous masses it has been 

 ascertained that three, at least, belong to the Lower Laurentian. 

 But. as we do not as yet know with certainty either the base or 

 the summit of this series, these three may be conformably fol- 



