574 



SCIENTIFIC RECREATIONS. 



mica, and felspar, which become crystallized by the excessive heat. For a 

 long time no traces of organisms could be detected in this or the Cam- 

 brian systems, but modern research has been rewarded with a little success. 

 The original deposits of micaceous gneiss, etc., have been altered, and many 

 true igneous rocks, such as syenite and granite, are found in them. These 

 very old rocks must have been originally deposited in strata converted by 

 heat and pressure into crystalline rocks. These rocks have been divided into 

 two series, under the names of lower and upper Laurentian. They are 

 metamorphic, and consist " mainly of gneiss interstratified with mica-schist, 

 with great beds of quartz, and massive beds of crystalline limestone, of which 



Fig 647. Upward Granite (Section). 



s 



Fig. 648. Conformable Strata. 



Fig. 649. Unconformable Strata 



one varies from 700 to 1,500 feet in thickness. Conglomerates also occur, 

 and there are vast deposits of magnetic and specular iron. Graphite, or 

 blacklead, is disseminated in strings, veins, and beds through hundreds of 

 feet of the lower Laurentian, and its amount is calculated by Dr. Dawson 

 to be equal in quantity to the coal seams of an equal area of the carboni- 

 ferous rocks " (Nicholson). 



Hitherto, no distinctly recognisable fossil has been discovered, with 

 the important exception of the Eozobn Canadense, which has been pro- 

 nounced to have been a gigantic foraminifer, growing layer upon layer, 

 and thus forming reefs of limestone ; the subject, however, is still a matter 

 of dispute. The eozoon was discovered by Mr. J. M'Mullen in 1858 in 

 Canada. 



