96 Tin American Geologist. February, 1894 
dance of graphite iii the Laurentian rocks has caused many 
authors. Sir William Dawson among others,* to postulate the 
existence of cellular organisms, certainly aquatic and possibly 
terrestrial, during the long pre-Cambrian epochs. In regard 
bo the possible existence of these forms of life, he sa} T s : 
"The climate and atmosphere of the Laurentian may have been well 
adapted for the sustenance of vegetable life. We can scarcely doubt 
that the internal heat of the earth still warmed the waters of the sea, 
and these warm waters must have diffused great quantities of mists and 
vapors over the land, giving a moist and equable, if not very clear, at- 
mosphere. The vast quantities of carbon dioxide, afterwards sealed up 
in limestones and carbonaceous beds, must also have still floated in the 
atmosphere, and must have supplied abundance of the carbon, which 
constitutes the largest ingredient in vegetable tissues. Under these 
circumstances the whole world would have resembled a damp, warm 
greenhouse, and plants loving such an atmosphere could have grown 
luxuriantly. In these circumstances the lower forms of aquatic vege- 
tation and those that love damp, warm air and wet soil would have been 
at home. * * The Alga? may have attained to gigantic dimensions, 
and may have even ascended out of the water in some of their forms. 
*• * Comparatively simple cellular and tubular structures, now de- 
graded to the humble position of flat lichens or soft or corky fungi, or 
slender cellular mosses, may have been so strengthened and modified 
as to constitute forest trees." (pp. 17-18.) 
We have still further presumptive evidence of the existence 
of aquatic vegetation in early Cambrian and Paleozoic times 
in the presence of vast numbers of animal forms which we 
are justified in believing subsisted upon such vegetation. 
But while we may inferentially postulate the existence of 
Algae, it seems mure than likely that the greater majority of 
the fossils described as Algae are not such at all. This matter 
has been so often referred to, however, that it need not be 
discussed here. It is the intention to call attention to certain 
facts which have been noted by many observers in respect to 
the positions where the supposed Algae occur, and to discuss 
their value as geological guides. 
The fossils are nearly always found as elevations upon the 
lower surfaces of the rock, although it sometimes happens 
that they are upon the upper surface. It has also been fre- 
quently remarked that where they occur, other and un- 
doubted organic forms are absent. This is stated in the 
description of nearly every species and has been repeatedly 
^Geological History of Plants. New York, 1888, pp. 12-19. 
