102 THE DAWN OF LIFE 



It is interesting to notice here that the Laurentian rocks 

 thus interpreted show that the oldest known portions of our 

 continents were formed in the waters. They are oceanic sedi- 

 ments deposited perhaps when there was no dry land, or very 

 little, and that little unknown to us, except in so far as its 

 debris may have entered into the composition of the Lauren- 

 tian rocks themselves. Thus the earliest condition of the 

 earth known to the geologist is one in which old ocean was 

 already dominant on its surface ; and any previous condition 

 when the surface was heated, and the water constituted an 

 abyss of vapours enveloping its surface, or any still earlier con- 

 dition in which the earth was gaseous or vaporous, is a matter 

 of mere inference, not of actual observation. The formless 

 and void chaos is a deduction of chemical and physical prin- 

 ciples, not a fact observed by the geologist. Still we know, 

 from the great dykes and masses of igneous or molten rock 

 which traverse the Laurentian beds, that even at that early 

 period there were deep-seated fires beneath the crust ; and it 

 is quite possible that volcanic agencies then manifested them- 

 selves, not only with quite as great intensity, but also in the 

 same manner, as at subsequent times. It is thus not unlikely 

 that much of the land undergoing waste in the earlier Lauren- 

 tian time was of the same nature with recent volcanic ejections, 

 and that it formed groups of islands in an otherwise boundless 

 ocean. 



However this may be, the distribution and extent of these 

 pre-Laurentian lands is, and probably ever must be, unknown 

 to us ; for it was only after the Laurentian rocks had been 

 deposited, and after the shrinkage and deformation of the 

 earth's crust in subsequent times had bent and contorted them, 

 that the foundations of the continents were laid. The rude 

 sketch map of America given in Fig. 3 will show this, and" will 

 also show that the old Laurentian mountains mark out the 

 future form of the American continent. 



