l: 



I it 



26 THE CHAIN OF LIFE. 



limestones which have become highly crystalline shows that it 

 is quite possible that the forms and structures of these organisms 

 may have been obliterated. 



Again, the Middle Laurentian abounds in carbon or coaly 

 matter. True, this is in the form of graphite or plumbago, 

 but this may be a result of metamorphism j and we 

 know that the carbon of coal-beds and bituminous shales of 

 much more modern times has been altered into graphite. 

 Further, the graphite occurs in the way in which we should 

 expect it to occur if of organic origin. It is found dissemi- 

 nated in the limestone, just as bituminous matter is found in 

 unaltered rocks of this kind. It xs found interlaminated with 

 gneiss, as carbonaceous and bituminous matters are found in 

 the shales of the ordinary fossiliferous rocks, where these 

 substances are known to be of organic origin. The graphite 

 also occurs in a very pure form in irregular veins, just as in 

 some bituminous formations the rock oil, oozing into fissures, 

 has been hardened into asphalt or coaly matter.^ 



To these facts may be added the presence of thick beds 

 and veins of iron ore and of apatite or calcium phosphate 

 (bone earth). Both of these substances occur in a dis- 

 seminated state in nearly all rocks, but they are concen- 

 trated into definite deposits by the action of life. Iron is 

 usually dissolved out and redeposited by acids produced in 

 the decay of vegetable matter, as we see in the clay iron- 

 stones of the coal formation and in bog-iron ores. Calcic 

 phosphate is taken up by many animals, and forms their shells 

 or skeletons, and is deposited on their death in beds on the 

 sea-bottom, sometimes to a very considerable extent. 



The concurrence of all these phenomena in the Middle 



^ Analyses recently made by Mr. C. Hoffman, of the Geological Survey 

 of Canada, show that beds of graphitic gneiss, some of them 8 feet in 

 thickness, contain as mnch as 25*5 to 30 per cent, of carbon, the remaining 

 earthy matter consisting principally of silica, alumina, and lime. The 

 graphite from veins was nearly pure carbon, containing from 97*6 to 99*8 

 per cent, of that substance. 





