TYPICAL LAURENTIAN AREA OF CANADA. 33 1 



its frequent stratified character, and the presence in it of lime- 

 stones and graphite indicating an approach to modern conditions 

 and the advent of life, together with the difficulty of clearly sep- 

 arating the two series from one another and defining their respect- 

 ive limits, lends support to this view. 



(2) A second view is that the Grenville Series is distinct from 

 the Fundamental Gneiss reposing on it unconformably and of 

 much more recent age ; that it consists of a highly altered 

 series of clastic origin — the Fundamental Greiss having possibly 

 some such origin as that mentioned under the last heading, or 

 representing a much older series of still more highly altered 

 sediments. This is supported by the fact that some observers 

 have thought they could in places trace out a line of contact 

 between the two. But in these cases it always becomes a matter 

 of serious doubt whether what has been considered to represent 

 the Fundamental Gneiss is not really a mass of intrusive rock, 

 in which, by pressure or motion, a somewhat gneissic structure 

 has been induced. If the Fundamental Gneiss, moreover, was 

 ever an ordinary sediment, it must have undergone a metamor- 

 phosis so profound that no trace of clastic origin remains, unless 

 the generally indistinct foliation or banding of some portions of 

 it be considered as such. It must also be noted in this connec- 

 tion that, althouech the rocks of the Grenville series are more 

 frequently possessed of a decided foliation and are often banded, 

 bands of different composition alternating with one another as 

 in ordinary sedimentary deposits, and although in this series 

 crystalline limestones and quartzites occur, we have as yet no 

 absolutely conclusive proof that even they are of sedimentary 

 origin. The series is thoroughly crystalline, most of its members 

 at least show the effect of great dynamic action, and so far as the 

 present writer is aware, no undoubted conglomerate or finer grained 

 rock showing distinct clastic structure has ever been found. In 

 view of this fact, — although the series is, in all probability, made 

 up in part at least and perhaps wholly of sedimentary material, 

 — the proposal to separate it from the rest of the Laurentian 

 and class it as Algonkian or Huronian seems at least premature. 



