120 ROYAL SOCIETY OF CANADA 



•entirel}' the limestones and associated strata, and tiiough along the outer 

 zone of the anoi-thosite areas a certain foliation is observed, which in 

 the gneisses was formerly regarded as proof of their sedimentary origin, 

 this foliation has evidently been induced by some other cause, and has no 

 relation to the planes of true sedimentation. 



The removal of the anorthosites from the position originally assigned 

 them as the upper member of the metamorphic sediments, in which cate- 

 gory the great mass of the Laurentian was formerly placed, renders the 

 rocks of that system divisible into two great parts, viz., the Fundamental 

 or Ottawa Gneiss, and the overlying series of giay quartzose gneiss, 

 •quartzite and limestone, which was included by Logan in the term G-ren- 

 ville series. This latter has for some years been regarded as constituting 

 the upper member of the Laurentian system. 



In this series, however, Logan included a great variety of rocks 

 which are now regarded as of igneous origin, among which may be men- 

 tioned large areas of pegmatite and other granites, pyroxenic rocks, 

 augen-gneiss, etc. Some of these, as in the case of the anorthosites, are 

 evidently newer than the limestones and other strata with which they 

 are associated. In point of fact, with the exception of the crystalline lime- 

 stones and certain limited areas of quartzite and gray gneiss, with which 

 these are usually associated, and which are well seen in some portions of 

 the country north of the Ottawa, more especially in the Gatineau district, 

 the rocks which may be regarded as strictly altered sediments are now 

 comparatively limited in extent. 



It would appear possible, therefore, to reduce the great series of the 

 so-called Laurentian rocks to two principal divisions, viz., a lower basal 

 or Fundamental Gneiss, in which all traces of sedimentation are wanting, 

 and which may be regarded as representing in altered form some portion 

 of the original crust of the earth ; and a newer secondary series, derived, 

 doubtless, fi-om the decay of the former, in which the evidences of clastic 

 origin are manifest. In connection with this second division another 

 group may be mentioned, which has a very considerable development, 

 <îhiefly to the west of the Ottawa, but is in close association with the 

 Grenville series. This has been styled by Vennor the Hastings series ; and, 

 while to some extent different in character from the rocks of the Gren- 

 ville division, notably in the presence of large areas of hornblcndic and 

 schistose rocks, it also in many respects presents a marked similarity in 

 the character of the gneisses and lime-atones. The Hastings roclcs, more- 

 over, furnish unmistakable evidence, in places, of sedimentation in the 

 presence of conglomerates and slates. It appears to be difficult, however, 

 to separate the two series to any great extent, though there are certain 

 portions of the Hastings which are much less highly metamorphosed than 

 the great mass of the Grenville rocks. Some of the limestones of the 

 Hastings are comparatively unaltered, being blue and slaty, but these, 



