80 



CANADIAN FOSSILS. 



> 



organism allied to Pyritonema of McCoy, a fossil similar to ■which Dr. 

 Nicholson has found in the Llandeilo of Hart Fell, near Moffat. 



Is it possible from so few facts to form any idea of the probable land-flora 

 of the great Silurian age, and oi its relation to that of the Devonian ? 

 I think it possible at least to arrive at some general notions on the subject, 

 ■which may be reduced to the following statements : 



1. It may be noted that no plants other than Lycopodiaceae or alUed 

 forms have been detected below the Lower Devonian. That this may 

 really indicate a greater antiquity of this family than any other is rendered 

 more probable by the fact that Lycopodiaceae increase in relative impor- 

 tance in descending from the Coal-formation to the Lower Carboniferous, 

 and thence into the Devonian and Upper Silurian, where they appear to be 

 left alone. Allowing for any possible amount of imperfection in the 

 record, this can scarcely be an accident. If, however, Eophyton expla- 

 natum should prove to be a land-plank allied to Nematoxylon, it may be 

 possible that prototypal Gymnosperms or Endogens may have extended 

 quite as far back in Geological time. 



2. Should it prove certain that Acrogenous plants allied to Lycopodia- 

 ceae, and perhaps such prototypes of Gymnosperms as Eophyton, extended 

 back to the Primordial period, then we might look for the actual origin of 

 land vegetation in the Laurentian. In a paper recently read before the 

 Geological Society,* I directed attention to the fact that in the Lauren- 

 tion of Canada vast quantities of carbon exist in the form of graphite. The 

 aggregate thickness of this matter is probably little inferior to that of coal 

 in the Carboniferous rocks. I also she ed that this graphite in its mode 

 of occurrence resembles that of bitumen and coaly matter in more modern 

 rocks, thatitis associated with organic limestoneand with deposits of iron ore, 

 probably of organic origin, and that under the microscope some portions of 

 it appear to show traces of vegetable fibre. Further, since we have in Rhode 

 Island beds of coal of the true Coal-formation in part converted into 

 graphite, and still retaining traces of organic structure, and since we 

 have in Canada abundance of instances of bituminous schists converted into 

 graphitic schists, there is no improbability in supposing that a similar change 

 may have passed on the carbon of the Laurentian. From these considera- 

 tions I deduced the conclusion that the Laurentian period was probably an 

 a»e of most prolific vegetable growth, and in which greai quantities of carbon 

 were fixed in the rocks of the earth's crust by this agency. Whether the 

 vegetation of the Laurentian was wholly aquatic or in part terrestrial we 

 have no means of knowing, but it is not unreasonable to conjecture that could 

 we find the Laurentian rocks in such condition as to show distinct organic 



• Journal of G«ol. Soc, Vol. XXYI, p. 112. 



