of
animals with which he lived. Many of these relics have been preserved
through thousands of years and frequently are brought to light. The
geological records are thus very important in throwing light upon the
antiquity of man. It is in the different layers or strata of the earth
caused by these changes that we find the relics of ancient life. The
earth thus reveals in its rocks and gravel drift the permanent records
of man's early life. Historical geology shows us that the crust of the
earth has been made by a series of layers, one above the other, and
that the geologist determining the order of their creation has a means
of ascertaining their relative age, and thus can measure approximately
the life of the plants and animals connected with each separate
layer.[7] The relative ages of fishes, reptiles, and mammals,
including man, are thus readily determined.

It is necessary to refer to the method of classification adopted by
geologists, who have divided the time of earth-making into three great
periods, representing the growth of animal life, determined by the
remains found in the strata or drift. These periods mark general
portions of time. Below the first is the period of earliest rock
formation (Archaean), in which there is no life, and which is called
Azoic for that reason. There is a short period above this, usually
reckoned as outside the ancient life, on account of the few forms of
animals found there; but the first great period (Paleozoic) represents
non-vertebrate life, as well as the life of fishes and reptiles, and
includes {75} also the coal measures, which represent a period of heavy
vegetation. The middle period (Mesozoic) includes the more completely
developed lizards and crocodiles, and the appearance of mammals and
birds. The animal life of the third period (Cenozoic) resembles
somewhat the modern species. This period includes the Tertiary and the
Quaternary and the recent sub-periods. Man, the highest being in the
order of creation, appears in the Quaternary period. Of the immense
ages of time represented by the geological periods the life of man
represents but a small portion, just as the existence of man as
recorded in history is but a modern period of his great life. The
changes, then, which have taken place in the animals and plants and the
climate in the different geological periods have been instrumental in
determining the age of man; that is, if in a given stratum human
remain