SOME EARLY MAMMALS 239 
researches on the history of camels as illustrated from fossil 
remains have brought to light another line of evolution equally 
interesting if not quite so complete. According to the latter 
palzeontologist, the very earliest ancestor of all the hoofed 
animals (and therefore of the horse) was the Eocene Phenacodus, 
with five toes. But this conclusion is not generally accepted 
now. 
We pass on to consider the true fossil horses, as worked 
out by Professors Huxley and Marsh, and others. The modern 
horse, and that which was known to man in the days before 
history was written, we may regard as a product of the latest 
geological period—the Pleistocene. The development of the 
horse from a primitive five-toed ancestor seems to have taken 
place along two separate lines, one in Europe and one in America, 
The latter is the most complete; for it so happens in that country 
the physical conditions which prevailed throughout nearly the 
whole of the Tertiary Era were singularly favourable to the 
preservation of the skeletons of those creatures which lived on 
land. The various members of the horse tribe that roamed over 
North America all through these long ages of the past were 
specially numerous in what is now the Rocky Mountain region, 
and their remains are sealed up in the strata of these regions. 
Here in Wyoming and Utah is found one of the oldest direct 
ancestors of the horse, the Orohippus of Marsh. During the 
middle Tertiary, or Miocene period, two other lakes existed on 
either side of the great Eocene basin. The largest of these, to 
the east of the Rocky Mountains, extended over portions of 
what are now Dakota, Nebraska, and Colorado. The clays 
deposited in this lake form the “ Bad Lands” of that region, 
so well known for their fossil treasures. The other Miocene 
lake was west of the Blue Mountains, where eastern Oregon 
