HURONIAN PERIOD. 511 



in quantity to the coal-seams of an equal area of the Carbon- 

 iferous rocks. 



Not only is the Lower Laurentian series of vast thickness 

 and greatly metamorphosed, but it must have been elevated 

 above the sea, and subjected to vast denudation, prior to the 

 deposition of the upper group. This is shown by the fact 

 that the Upper Laurentian lies unconformably upon the trun- 

 cated edges of the Lower Laurentian. The Upper Lauren- 

 tian group is about 10,000 feet thick, and consists wholly of 

 stratified crystalline rocks. These consist mainly of gneissic 

 and felspathic rocks, often characterised by the occurrence of 

 lime-felspar or Labradorite. The series is extensively devel- 

 oped in Labrador, and is sometimes spoken of as the " Labra- 

 dor series." 



In Britain it has been conjectured, with great probability, that 

 the "fundamental gneiss" of the Hebrides and the "hypers- 

 thene rocks " of the Isle of Skye belong to the Laurentian series. 



LIFE OF THE LAURENTIAN PERIOD. The Laurentian rocks 

 are often spoken of as the Azoic series (Gr. a, without ; zoe, 

 life) ; but the name appears to be inappropriate, because there 

 is good evidence to show that living beings were in existence 

 in the Laurentian period. In the first place, it is certain that 

 the Laurentian rocks, though now highly metamorphic, were 

 originally deposited as ordinary sedimentary beds of sandstone, 

 conglomerate, shale, and limestone. There is, therefore, no 

 reason whatever for supposing that the seas of the Laurentian 

 period differed in any respect from modern seas, so far at any 

 rate as to render the existence of living beings impossible j 

 while we know that one of the results of metamorphic action 

 is the obliteration of the fossils in the rock affected. Secondly, 

 by the researches of Sir William Logan there was discovered 

 in one of the limestones of the Lower Laurentian group, the 

 body which has been described under the name of Eozoon 

 Canadense, and which is believed to be a gigantic Foraminifer. 

 The organic nature of this body was first detected by Dr Daw- 

 son of Montreal, and his opinion as to its nature has since 

 been confirmed by the highest authorities. Thirdly, there is 

 good reason to believe that the graphite of the Laurentian 

 rocks is nothing more than metamorphic coal, and that it is 

 derived from vegetables which flourished during the Lauren- 

 tian period. 



HURONIAN PERIOD. 



The rocks of the Huronian series rest unconformably upon 

 the denuded edges of the Laurentian rocks on the borders of 



