ANCIENT LIFE ON THE EAKTH 15 



origin, and probably represents the more or less 

 altered remains of the original crust of the earth. 

 The upper formation consists of limestones and 

 clastic rocks, evidently of aqueous origin, which are 

 called the Grenville and Hastings series. The 

 argillaceous beds interstratified with the limestones 

 have been changed into a rock, which is also called 

 gneiss, although different in chemical composition 

 from the fundamental gneiss. The Grenville series 

 is supposed by Messrs. Adams and Barlow, of the 

 Geological Survey of Canada,* to have been deposited 

 at a time when the fundamental gneiss, which 

 formed the bed of the ocean, was in a semi-molten or 

 plastic condition, and the sediments sank down into 

 the gneiss, so that in places they were entirely 

 enwrapped by it. It is in this Grenville series that 

 a structure called Eozodn canadense has been found. 

 It was the microsopic characters of Eozodn the 

 regular concentric layers of which it is generally 

 composed which first gave rise to the idea that it 

 was of organic origin. But these regular layers are 

 sometimes very few in number, the greater part of 

 the supposed organism being quite irregular in 

 structure ; indeed some specimens are without any 

 arrangement at all, and have been called Archceo- 

 spherince, under the idea that they belonged to a 

 different genus to Eozodn. In its microscopic 

 appearance Eozodn must closely resemble some of 

 the Foraminifera, or it could not have deceived such 

 experienced observers as Dr. Carpenter and Pro- 



*American Journal of Science and Art, Ser. 4. vol. iii., 

 p. 173. 



