170 JR. S. Lull — The Evolution of the Horse Family. 



glimmerings of life coming to us not as remains showing form 

 and structure, but as graphite, limestones, and iron ores, which 

 are the chemical effects of organic life. This period is of vast 

 duration ; then, almost suddenly, myriads of forms of lowly 

 organization appear, out of which are slowly evolved animals 

 and plants of higher and yet higher types. 



At length, when the plants had sufficiently spread over the 

 land, there gradually emerged from the waters animals cajmble 

 of breathing the air, among them creeping amphibians like 

 the salamanders of today. From these arose the lowly reptiles, 

 but during the long period known to geologists as the Paleo- 

 zoic seon no higher forms of life appear. Then followed the 

 Mesozoic aeon, when reptiles flourished, out of which arose the 

 higher animals, both birds and mammals. Mammals lived 

 during the Mesozoic, probably in abundance, but our record 

 of them is very meager, doubtless owing to the conditions 

 under which they existed. In the Cenozoic aeon, the age of 

 mammals, the geological record is rich and easily decipherable. 



In the basal strata of the Cenozoic age the mammals appear 

 in great profusion, variety, and some of considerable size, 

 indicating a migration from a region as yet unknown. Among 

 these early mammals no horselike ancestors have been yet dis- 

 covered, undoubted horses first appearing in the genus Hyraco- 

 therium from the London Clay of England, the ancestor of 

 Eohippus. 



The sequence of genera is given in the table on p. 169. 



Part II. 



Synopsis of the Geological History of Horses. 



EOCENE PEEIOD. 



During Eocene times North America was clad with forests 

 in which grew both evergreen and deciduous trees distinctly 

 modern in character. The moist climate gave rise to many 

 streams and lakes, along the shores of which grew sedgy 

 meadows that in turn gave rise to grassy plains. These were the 

 conditions under which the horses made their first appearance, 

 and the increasing development of grass lands gave the initial 

 trend to their evolution. 



During the earlier ages of the Eocene period there was but 

 little differentiation on the part of the various mammalian 

 orders, and the ancestral horse is here unrecognized or undiscov- 

 ered. The earliest known horses appear in the rocks of the 

 Wasatch age, and while they are found in both the Old and the 

 New Worlds the more primitive are of the former, as shown in 



