Ales Hrdlicka 
Skeletal Remains Suggesting or Attributed to Early Man in North America [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. According to current classification of geological time the Ceno zoic era (the era of modern life) is divided into two periods, the Tertiary and the Quaternary. The former, which is the older, comprises three subdivisions, Eocene, Miocene, and Pliocene, and the latter two subdivisions, Pleistocene and Recent. These periods are indicated in figure 1 in the order of the formations representing them.