THE FOUNDATIONS OF THE CONTINENTS 93 



and sometimes ten to twelve feet thick. The 

 occurrence of this large amount of carbon warrants 

 us in supposing that it represents a vast vegetable 

 growth, either on the land or in the sea, or both. 



In like manner, in later geological periods, beds 

 of iron ore are generally accumulated as a conse- 

 quence of the solvent action of acids produced by 

 vegetable decay, as in the clay ironstones of the 

 coal formation and the bog iron ores of later times. 

 Thus the beds of magnetic iron occurring in the 

 Upper Laurentian may be taken as evidences, not 

 of vegetable accumulation, but of vegetable decay. 



May not also the great quantity of calcium phos- 

 phate mined in the Grenville series in Canada, 

 indicate, as similar accumulations do in later forma- 

 tions, the presence of organisms having skeletons 

 of bone earth ? 



With reference to the carbon and iron ore of 

 the Grenville series, I may quote the following from 

 a paper published in the Journal of the Geological 

 Society of London in 1870 : — 



"The quantity of graphite in the Upper Lauren- 

 tian series is enormous. In a recent visit to the 

 township of Buckingham, on the Ottawa River, I 

 examined a band of limestone believed to be a 



