98 RELICS OF PRIMEVAL LIFE 



decay of plants. In this case such great ore beds 

 as that of Hull, on the Ottawa, 70 feet thick, 

 or that near Newborough, 2(X) feet thick,^ must 

 represent a corresponding quantity of vegetable 

 matter which has totally disappeared. It may be 

 added that similar demands on vegetable matter 

 as a deoxidizing agent are made by the beds and 

 veins of metallic sulphides of the Laurentian, though 

 some of the latter are no doubt of later date than 

 the Laurentian rocks themselves. 



" It would be very desirable to confirm such con- 

 clusions as those above deduced by the evidence of 

 actual microscopic structure. It is to be observed, 

 however, that when, in more modern sediments, 

 algcTe have been converted into bituminous matter, 

 we cannot ordinarily obtain any structural evidence 

 of the origin of such bitumen, and in the graphitic 

 slates and limestones derived from the metamor- 

 phosis of such rocks no organic structure remains. 

 It is true that, in certain bituminous shales and 

 limestones of the Silurian system, shreds of organic 

 tissue can sometimes be detected, and in some 

 cases, as in the Lower Silurian limestone of the 



^ " Geology of Canada," 1863. 



