343 PROCEEDINGS OF SECTION C. 
We know as a fact that the earth is a hot body travelling 
through space which is intensely cold. It must, therefore, be 
cooling. Consequently, in the early days of its history, it must 
have been very much hotter than it is now. There are, indeed, 
reasons for thinking that at a very remote period the earth was 
actually molten owing to the intense heat, when, of course, the 
whole of the water of the ocean must have been in a state of 
vapour, and formed part of the atmosphere. As the temperature 
lowered, this aqueous vapour would condense and fall on the 
surface of the earth as hot rain. The first ocean would, therefore, 
be almost at its boiling-point, and would gradually cool down ; 
but no life could exist in the ocean or on the land while the tem- 
perature much exceeded 200° F., which, so far as we know, is the 
highest temperature in which plants can live. This period of the 
hot ocean was, therefore, the Azoic era of the earth’s history 
which, as the cooling progressed, passed into the Protozoic and 
then into the Paleozoic era, which includes the Cambrian period. 
At first the ocean must have been nearly uniform in temperature 
from the equator to the poles ; but climatic zones appear to have 
been established in the Silurian period, if not earlier. 
The pre-Cambrian rocks have received various names in different 
parts of the world ; but, as they are better developed and more 
easy to decipher in North America than elsewhere, it is probable 
that so soon as the officers conducting the geological surveys of 
Canada and the United States agree on a classification and a 
nomenclature, it will be universally adopted. At present this is 
not the case, and, in this address, I have followed for the most 
part the Canadian authorities who first discovered these rocks, 
and who have for many years devoted an immense amount of 
labour to mapping them. 
The oldest rock system known to us is composed chiefly of gneiss, 
sometimes passing into granite, and it probably represents the 
Azoic era. It is called the Laurentian system. Above it, in 
discordant sequence, is found in Canadaa series of schists, arkoses, 
quartzites, greywackes, and schistose conglomerates called the 
Huronian system, which probably represents the Protozoic era. 
However, in order to avoid using theoretical names, which may 
be incorrect, the Laurentian and Huronian are called collectively 
the Archean era. 
Immediately above the Huronian there is a great unconformity, 
marking a considerable interval of time, and the succeeding rocks 
are called Keweenewan in Canada and Algonkian in the United 
States. They are composed of a great thickness of sandstones and 
slates—sometimes locally altered into schists—which underlie the 
Cambrian system, the base of which is marked by what is known 
as the Olenellus fauna, from the occurrence in it of the trilobite 
called Olenellus. Let us look at these more in detail. 
