Page:Popular Science Monthly Volume 44.djvu/632

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WITHIN a comparatively short time our knowledge of man's existence upon the earth has been greatly increased. By the aid of monuments, language, man's handicraft in stone, brass, bronze, and iron in constructing implements of warfare and husbandry, the anthropologist has been able to classify prehistoric man into ages—namely, the chipped stone or palæolithic, the polished stone or neolithic, the brass, the bronze, and the iron ages.

The purpose of this paper is to deal with the evidence of the earliest of these. The records are to be found in Nature's infallible history of the world's development printed on pages of rock in fossil type. In order that those present not conversant with geology may more clearly understand what is to follow, it will perhaps be well to briefly explain the order and arrangement of these pages of rock.

To carry out the simile, we might say that this great history is written in three volumes—the first and earliest called Palæozoic or Primary; the second, Mesozoic or Secondary; and the third, Kainozoic or Tertiary. The first volume, or Palæozoic, is divided into three books, each book treating of the flora and fauna which existed at the time of which it speaks. The first book is called Silurian, and treats of that part of the age when invertebrates predominated; the second, Devonian, and treats of that part of the age when fishes predominated; the third. Carboniferous, and treats of that part of the age when coal plants predominated. The second volume, or Mesozoic, is a record of the times when reptiles predominated. The third volume, Kainozoic, is a record of the times when mammals predominated.

It must be understood that there is no clear-cut line of demarcation separating the life of these ages, some of the forms of the earliest existing to-day, others having become extinct, the orders of life named with each age being simply the predominating life of the period. All these periods are divided into many minor subdivisions. Man being a mammal, we are, however, interested only in the subdivisions of the Kainozoic or Tertiary. This period, beginning with the earliest, is divided into Eocene, Oligocene, Miocene, Pliocene, and Post-Pliocene or Post-Tertiary, also called Quaternary. For the purposes of this subject we are interested mainly in the Post-Pliocene or Quaternary, which some

  1. A lecture delivered May 12, 1893, in the Popular Course before the Academy of Natural Sciences, Philadelphia.