THE AMERICAN BISONS. 235 
there is the same conspicuous absence of the remains of this animal. These 
evidences, negative and incomplete as they are, make it at least probable 
that the buffalo was unknown to the people who built. the mounds and pre- 
ceded the tribes which were found here, by the whites, in the seventeenth 
century. The same arguments warrant us in supposing that the Bison lali- 
frons, with its contemporaries, — the musk ox, the elephant, and the masto- 
don,—had vanished before the advent of this race, or at least before the 
time of which we have evidence in the. fossils already found. 
I have long been of the opinion, without claiming originality therein, that 
the tribes which built the mounds and the shapely measured forts of this 
region were driven to the southward by an invasion of other tribes. coming 
from the northward and northwestward. In the Memoirs now in preparation, 
concerning the ancient peoples of this region, it will be claimed, on what 
seems to Mr. Lucian Carr, ethnologist of tle Survey, and to myself, sufficient 
evidence, that these mound-building peoples were essentially related to the 
Natchez group of Indians, and were driven southward by the ruder tribes 
of the somewhat related tribes which occupied the northern parts of the 
Mississippi Valley, when we first knew it. All this seems to me to have a 
possible significance in the problem of the coming of the buffalo; when we 
remember that the Indians north of the Ohio were much in the habit of 
burning the forests, and so making open plains, or prairies, and that, as Mr. 
Allen has well pointed out, the buffalo cannot penetrate far into the denser 
forests, it may be that it was this destruction of forests that laid the way 
open to their entrance. The so-called Barrens of Kentucky, the southward 
extension of the Wabash prairies, give us evidence on this point. As soon as 
the Indians were driven away, these Kentucky prairies sprang up in timber, 
and are now densely wooded. The same is in part true of the other prairies 
of the Ohio Valley. I am inclined to think that the forcing back of the 
timber line from the Mississippi is principally due to the burning of the 
forests by the aborigines in their eastward working, aided by the continued 
decrease of the rainfall, which I believe to have been a concomitant of the 
disappearance of the glacial period.* The question of the origin of the buf 
falo and its relation to the earliest tribes of people in this district is made 
still more complicated by the fact that there is no doubt that there was an 
earlier and closely related species of buffalo in this district, probably coeval 
with the mammoth and mastodon, and possibly with the caribou and elk, 
* Notes on the cause and geological value of variations in rainfall. Vol. XVII, p. 176, et seg. Pro- 
ceedings of the Boston Society of Natural History. 
