LIGHT, LUMINARIES AND LIFE. 189 
another sense) is the basis of protoplasm.” That power of 
building up the mineral constituents of our planet into living 
material,* is a function which animals in general do not 
possess. There seems to be little room therefore for doubt 
that the earliest living cells belonged to the vegetable kingdom. 
In the early Cambrian rocks, there is evidence of a practical 
differentiation of the animal from the vegetable ; and we must 
suppose that the lowest forms of animal life began to feed upon 
vegetable matter, only as yet elaborated into very simple forms, 
and for a length of time attaining to no higher development 
than that of cellular cryptogams (alge, lichens, etc.). Some 
light was needed for this, but not very strong light, such as 
we receive from the direct rays of the sun. In fact, reasoning 
from what we can actually observe of the conditions most 
favourable to the reproduction and development of such low 
living forms, we may safely infer that a permanent diffused 
light, accompanied by warmth and moisture, such as prevailed 
upon the earth universally in very early times, would be most 
favourable to the organic advance at that stage. And there is 
plenty of evidence to show that such conditions prevailed on 
this globe through the Cambrian and Silurian periods of its 
history ; and toa less degree during the Devonian and Carboni- 
ferous periods, when the great developments of continental 
regions were outlined along with the permanent ocean basins, 
after our planet had passed through that stage of planetary 
development, during which there was practically a universal 
ocean,t retarding the cooling of the lithosphere, owing to the 
non-conductivity of water for heat. though allowing of trans- 
mission of heat upwards by convection currents. The physical 
conditions under which the enormous development of vascular 
cryptogams characteristic of later Paleozoic time took place, 
were—we may fairly believe—those of warmth and a moist 
atmosphere surcharged with CO, with the further alteration 
* But everywhere in the presence of the elements of water. Lionel 
Beale, Trans. Vict. /nst., vol. xxxiv. 
+ In the Guardian (Nov. 6th, 1907) Professor Driver made his 
professorial confrére Professor Sollas to say, in his characteristic manner, 
“Geologists know nothing of an universal ocean.” It was easy to 
answer him, as I did; but he was made to contradict himself, when he 
endorsed, as ‘accepted universally by all geologists” (cbid., Nov. 27th, 
1907), the “table of succession of life on this globe” (oc. cit.), from 
which no other inference than the “ universal ocean” view is deducible 
as I pointed out then (cbid., Dec. 4th, 1907). 
t “Surcharged,” as compared with the present atmosphere. 
