90 THE CHAIN OF LIFE. 



portions of the Laurentian carbon retaining traces of organic 

 structure. My own observations, though somewhat numerous, 

 allow me only to say that the graphite sometimes presents 

 fibrous forms, that it occasionally appears as vermicular threads 

 — which, however, I suppose to be fillings of canals of Eozoon 

 — and that in the graphitic beds there are occasionally slender 

 root-like bodies of a lighter colour than the mass ; but none of 

 these indications are sufficient to determine anything as to its 

 vegetable origin, or the nature of the plants from which it may 

 have been derived. 



In any case, the quantity of carbon which has been accumu- 

 lated in the Laurentian rocks is very great. I have measured 

 one bed at Buckingham, on the Ottawa, estimated to contain 

 20 per cent, of carbon, and which is at least eight feet in 

 thickness. Sir William Logan has described another similar 

 bed from ten to twelve feet thick, and more recent reports of 

 the Geological Survey of Canada mention a bed supposed to 

 be twenty-five feet thick, in which Mr. Hoffman finds 30 

 per cent, of carbon. On the whole the quantity of carbon in 

 the graphitic zone of the Laurentian is comparable with that 

 in certain productive coal-fields, and we certainly have in the 

 subsequent geological history no examples of such accumu- 

 lations except from remains of the luxuriant vegetatipn of 

 swampy flats. 



The Upper Laurentian and Huronian have as yet afforded 

 no evidence of land vegetation. The Cambrian, as already 

 stated, abounds in remains of sea-weeds ; but though the forms 

 which have been named Eophyton have been regarded as land 

 plants, this claim is, to say the least, very doubtful ; and I have 

 as yet seen nothing of this kind which did not appear to me to 

 be merely markings made by objects drifted over the bottom 

 or remains of marine plants. Yet in the Upper Cambrian there 

 are wide surfaces of littoral sandstone often containing minute 

 carbonised fragments, and which might be expected to afford 

 indications of land vegetation, had such existed. I have myself 



