lions of years every one is always a little surprised, and I might say very briefly 

 and parenthetically why we give this as the approximate period. It depends 

 entirely upon the average rate of the deposition of rock, sandstone and gravel, 

 in the mouths of streams of considerable size. In the delta of the Mississippi, 

 for instance, the average rate of deposition in the gulf near land is about one 

 foot in one hundred years ; very near land it is much more rapid, and farther 

 out, less rapid. One foot in one hundred years is a rather rapid rate of deposi- 

 tion. There are so many thousands of feet of rock which have been deposited 

 above the remains of this ancestral horse, that we calculate it would require at 

 least three millions of years for their deposit, and that is a rather conservative 

 estimate. At the same time, you must take these estimates with a pinch of salt; 

 that is, not too literally, because there is always a margin of error one way or 

 the other. 



Here we have one of the descendants of our little horse which is called the 

 forest type of horse, for the reason that its teeth are rather short crowned, 

 and are adapted to browsing rather than grazing; secondly, its feet are rather 

 of the spreading type, as you see by the fact that the lateral toes (which now 

 begin to start on their long journey toward the degenerated condition which 

 we know as splint bones) still rest upon or near the ground, as seen for example 

 in the right hind foot. This is one of the first horses found with the Whitney 

 fund. The rear view of this animal brings out the fact that the four toes have 

 now given place to three; the median toe is somewhat enlarged, the lateral toes 

 are more like claws, and they only reach the ground when the animal is walking 

 in comparatively soft or marshy places. We therefore imagine that this type 

 of horse was one which, rather than seeking its food in the plains, retained the 

 remote ancestral habit of living in the forests, remaining a browser. Fig. 12. 



In the Miocene geological period, half way between the Eocene, which 

 we first looked into, and the present time, the horses are found in Florida, in the 

 plains region east of the Rocky Mountains, in Montana, in certain parts of Europe, 

 in the Italian Peninsula, at the head of the Persian Gulf, and in France. But 

 it is noteworthy that the horses which are found in the old world at this period 

 are of such a structural type that they are excluded from being considered as 

 the ancestors of the true horse; whereas in North America we find three types 

 of horses, the 'forest type' which we have just seen ; the second type, the 'desert 

 type' of most beautiful and delicate and graceful build, more like the deer than 

 the horse, which also became extinct; and a third type, transitional between the 

 two, the Protohippus, which most closely corresponds to what we believe to be 

 the middle stage in the evolution of the true horse. 



Of the 'desert type,' is a horse discovered in northeastern Dakota, in a 

 most interesting way. This animal, as we recognize by the small size of the 

 tusks, was a mare, and with it were found the skeletons of two young horses, 

 with their limbs closely drawn up beneath the body, the skull thrust down be- 

 tween the fore legs in each case, indicating that these three animals had been 

 seeking shelter together either from a sand or wind storm, or from an 

 exceptionally cold wave, and had perished in this position, huddled up, as it 

 were, to protect themselves against some force of nature. Hundreds of thous- 

 ands of years have elapsed, and these animals were fortunately uncovered by 



