CHAPTER XLV. 



THE MESOZOIC SYSTEM THE TRIASSlO, OOLITIC, AND CRETACEOUS FOR- 

 MATIONS THE EOCENE, MIOCENE, AND PLIOCENE THE GLACIAL 



PERIOD PRE-HISTORIC MAN. 



WE trust that the general reader has gleaned from the foregoing chapter 

 some few ideas concerning the growth of plant and animal life in the early 

 periods of the world's existence. From the Laurentian System we have 

 briefly traced the conformation of the globe at the dawn of organic life 

 through the Silurian Old Red Sandstone and Carboniferous formations, 

 indicating as we proceeded the chief points in the world's history, and the 

 gradual development of life through many ages. There is no real or bold 

 line of demarcation drawn between these systems. As seam unites to seam, 

 and layer to layer, stratum upon stratum, so the systems almost insensibly 



Fig. 670. Fossils of the Trias Group. 



1. Ammonites nodosus. 3. Possidonia minuta. 



2. Avicula socialis. 4. Encrinites moniliformis. 



unite, and forms of life appear, mature, and die away as the babe grows into 

 the man, and dies away again to old age and final extinction. So one 

 system merges into another, each and all a factor in the great work which 

 was intended to prepare the earth for the greatest and latest development 

 of Nature MAN ! 



But all this while the earth had been, as it still is, undergoing continual 

 change. Sometimes gradually, in the wearing away, or elevation of beach 

 or headland ; sometimes suddenly, as when mighty hills were upheaved and 



