1870.] DAWSON— LAURENTIAN GRAPHITE. 19 



group, and are separated from it by beds having the character of 

 the Huronian. 



There is thus no absolute impossibility that distinct organic 

 tissues may be found in the Laurentian graphite, if formed from 

 land-plants, more especially if any plants existed at that time 

 having true woody or vascular tissues ; but it cannot with certainty 

 be affirmed that such tissues have been found. It is possible, how- 

 ever, that in the Laurentian period the vegetation of the land may 

 have consisted wholly of cellular plants, as, for example, mosses 

 and lichens ; and if so, there would be comparatively little hope 

 of the distinct preservation of the forms or tissues, or of our being 

 able to distinguish the remains of land-plants from those of AlgaB. 



We may sum up these facts and considerations in the following 

 statements : — First, that somewhat obscure traces of organic struc- 

 ture can be detected in the Laurentian graphite ; secondly, that 

 the general arrangement and microscopic structure of the substance 

 corresponds with that of the carbonaceous and bituminous matters 

 in marine formations of more modern date ; thirdly, that if the 

 Laurentian graphite has been derived from vegetable matter, it 

 has only undergone a metamorphosis similar in kind to that which 

 organic matter in metamorphosed sediment of later age has ex- 

 perienced ; fourthly, that the association of graphitic matter with 

 organic limestone, beds of iron ore, and metallic sulphides greatly 

 strengthens the probability of its vegetable origin ; fifthly, that 

 when we consider the immense thickness and extent of the Eozoonal 

 and graphitic limestones and iron-ore deposits of the Laurentian, 

 if we admit the organic origin of the limestone and graphite, we 

 must be prepared to believe that the life of that early period, 

 though it may have existed under low forms, was most copiously 

 developed, and that] it equalled, perhaps surpassed, in its results, 

 in the way of geological accumulation, that of any subsequent 

 period. 



In conclusion, this subject opens up several interesting fields of 

 chemical, physiological, and geological inquiry. One of these 

 relates to the conclusion stated by Dr, Hunt as to the probable 

 existence of a large amount of carbonic acid in the Laurentian 

 atmosphere, and of much carbonate of lime in the seas of that 

 period, and the possible relation of this to the abundance of 

 certain low forms of plants and animals. Another is the compari- 

 son already instituted by Professor Huxley and Dr. Carpenter, 

 between the conditions of the Laurentian and those of the deeper 



