304 SPARKS FROM A GEOLOGIST'S HAMMER. 



This, I say, was the conviction which became wide- 

 spread among paleontologists in consequence of the chain 

 of discoveries announced by Professor Marsh, from which 

 it appeared that at least seven generic modifications of 

 the horse-type had lived successively upon our continent.* 



The very fact of the reality of so gently graduated a 

 succession was deemed by Professor Marsh adequate ground 

 for assuming that all these horse-types belonged to one 

 line of descent, with some lateral ramincations.f To me, 

 while admitting the high probability that the genealogical 

 relationship was a fact, it seemed that the simple circum- 



* These were: 1. Orohippus, of the Middle Eocene; size of fox, and with 

 four toes before and three behind; 2. Epihippus (a later discovery, however), 

 from the Later Eocene, resembling Orohippus generally, but differing in the 

 teeth ; 3. Mesohippus, from the Oldest Miocene ; size of sheep, having three toes 

 before and three behind, and with large " splint " bones before ; 4. Miohippus, 

 from the Late Miocene; size of sheep, with three toes and small splints before, 

 and three unequal toes behind, the lateral being diminished; 5. Protohippus, 

 from the Early Pliocene; size of ass, having the lateral toes in each foot reduced 

 to dangling hooflets ; 6. Pliohippus, of Middle Pliocene ; size of small horse, and 

 having single toes with large lateral splints; 7. Equus, the genus of the domestic 

 horse, known in America (Equus excelsus, at least) as early as the Later Pliocene, 

 and in Europe (Equus fossilis, probably not distinct from the 'domestic species) 

 in the Cavern Epoch of the Quaternary. In Equus the functional toes are re- 

 duced to the middle digit on each foot, but the rudiments of the two contiguous 

 ones still remain as " splints." At a later date (1876) Professor Marsh discovered 

 a still older equine, Eohippus, from the Oldest Eocene; size of a fox, with four 

 functional toes before and three behind, like Orohippus, but with rudiments of a 

 fourth toe behind, and hence, it is inferred, the rudiments of a fifth toe in front. 

 The hoofs were mere thick, broad and blunt claws. The Anchippus and Euro- 

 pean Hipparion (Hippotherium in America) were closely related to Protohippus^ 

 while Merychippus was probably identical. Anchippus, Hipparion and Stylonus 

 constituted a collateral series diverging from the equine stem. Anchitherium, 

 from the older Miocene, and the oldest equine known in Europe, is similar to our 

 MiohippuS) but a little less specialized. It, or its immediate predecessor, proba- 

 bly carried this type from America in early Miocene times, after equines had 

 been flourishing in the u New " World for a whole geological period. 



+ The same weight was afterward given to this class of evidence in Marsh's 

 address as Vice-President of the American Association, at the Nashville meeting, 

 in 1877. It may also be here stated that Professor Huxley had similarly assumed 

 that this single line of evidence closed the door to all future argument or dubita- 

 tion. This was in his New York lectures, in 1876, of which I have something 

 further to say in another chapter. 



