634 REPORT— 1897.. 



Fundamental Gneiss itself, or upon rocks occupying its position and very similar 

 to it in character. There can be no reasonable doubt that the mass of what now 

 constitutes the Fundamental Gneiss originally existed as the floor upon which the 

 Huronian was deposited. 



The name Archaean has been adopted and employed by the Geological Survey 

 of Canada in the sense in which it was introduced (in 1874), and consistently 

 maintained by Dana — i.e. to include all rocks below the great hiatus of which 

 evidence was first found in the Lake Superior region. The author of the name 

 never assented to its restricted application as proposed by Irving and followed by 

 Van Hise and others, and as a synonym for the Fundamental Gneiss or ' Base- 

 ment Complex ' it is not only unnecessary but is scarcely etymologically correct, if 

 we admit that a part of the ' Complex ' is of comparatively late date. 



We have reached a point at which we may ask what is now our conception of 

 these Archaean rocks in Canada, and more particularly in the great Protaxis, as 

 resulting from the most recent investigations of a critical kind. The reply may 

 be given briefly from the latest reports of those still at work on the problems 

 involved as follows : — 



The Laurentian comprises (1) the Fundamental Gneiss or Lower Laurentian 

 (also referred to as the Ottawa Gneiss or Trembling Mountain Gneiss in older 

 Keports), and (2) the Grenville Series. An important part of the gneisses of the 

 GrenviUe Series has been shown by chemical analysis to be identical in composition 

 with ordinary Palaeozoic argillites, and they are interbedded with quartzites and 

 massive limestones, also evidently of aqueous origin, and in some places abounding in 

 graphite. These beds are, however, closely associated with other gneisses in which 

 orthoclase largely preponderates that have the composition of igneous rocks. The 

 Fundamental Gneiss consists chiefly, if not exclusively, of rocks of the last-named 

 class, the banding or foliation of which, though now generally parallel to that of 

 the Grenville Series, has probably been'produced mainly or entirely by movements 

 induced by pressure, in a mass originally diflering more or less in composition in 

 its difi'erent parts. The two series are sometimes separable on the ground locally, 

 but with difficulty ; in other places they cannot be clearly defined.* 



The Upper Laurentian, Labradorian, Norian or Anorthosite group, maintained 

 for a number of years on the evidence already mentioned, is found to consist 

 essentially of intrusive rocks, often foliated by pressure, later in age than the 

 Grenville Series, but in all probability pre-Palaeozoic. 



The Ruronian comprises felspathic sandstone or greywacke more or less 

 tufaceous in origin, quartzites and arkoses passing into quartzose conglomerates 

 and breccia conglomerates, often with large fragments of many different varieties 

 of granite, syenite, &c., diorite, diabase, limestones, and shales or slates chang- 

 ing to phyllites in contact with the numerous associated igneous masses. 

 Over wide areas altered greenstones and their associated tuff's preponderate, 

 often with micaceous, chloritic, serlcitic and other schists, many of which ai'e 

 of pyroclastic origin, although some may represent ordinary aqueous deposits, and 

 all have been much affected by subsequent dynamic metamorphism. 



The Huronian rocks have not yet been found in distinct relation to those of 

 the Grenville Series, but are generally in contact with the Fundamental Gneiss, in 

 the manner previously alluded to. Where not composed of volcanic material it 

 appears to be largely of a littoral character, while the Grenville Series seems 

 rather to indicate oceanic conditions. 



No reference has so far been made to the development of Archaean rocks, known 

 as the ' Hastings Series.' The rocks thus named occupy considerable tracts to the 

 south of the Ottawa Eiver, west of the City of Ottawa. They were originally 

 classed by Logan and Murray with the Grenville Series of the Laurentian, although 

 Murray soon after insisted on their peculiar features, and they came to be recog- 

 nised by the above geographical name during subsequent discussions as to their 

 systematic position, by the authors above referred to, and by Hunt, Venuor, and 

 Macfarlane. These rocks are particularly alluded to now, because later work 

 seems to show that both the Grenville Series and the Huronian are represented in 



' Cf. Adams, Annual Jleport Geological Survey of Canada, 1895. 



