Buffaloes are very fond of rolling in dry dirt or even in mud, and this habit is quite strong in captive animals. Not only is it indulged in during the shedding season, but all through the fall and winter. The two live buffaloes in the National Museum are so much given to rolling, even in rainy weather, that it is necessary to card them every few days to keep them presentable. Bulls are much more given to rolling than the cows, especially after they have reached maturity. They stretch out at full length, rub their heads violently to and fro on the ground, in which the horn serves as the chief point of contact and slides over the ground like a sled-runner. After thoroughly scratching one side on mother earth they roll over and treat the other in like manner. Notwithstanding his sharp and lofty hump, a buffalo bull can roll completely over with as much ease as any horse. The vast amount of rolling and side-scratching on the earth indulged in by bull buffaloes is shown in the worn condition of the horns of every old specimen. Often a thickness of half an inch is gone from the upper half of each horn on its outside curve, at which point the horn is worn quite flat. This is well illustrated in the horns shown in the accompanying plate, fig. 6. [Illustration: DEVELOPMENT OF THE HORNS OF THE AMERICAN BISON. 1. The Calf. 2. The Yearling. 3. Spike Bull, 2 years old. 4. Spike Bull, 3 years old. 5. Bull, 4 years old. 6. Bull, 11 years old. 7. Old "stub-horn" Bull, 20 years old.] Mr. Catlin[36] affords some very interesting and valuable information in regard to the bison's propensity for wollowing in mad, and also the origin of the "fairy circles," which have caused so much speculation amongst travelers: [Note 36: North American Indians, vol. I, p. 249, 250.] "In the heat of summer, these huge animals, which no doubt suffer very much with the great profusion of their long and shaggy hair, or fur, often graze on the low grounds of the prairies, where there is a little stagnant water lying amongst the grass, and the ground underneath being saturated with it, is soft, into which the enormous bull, lowered down upon one knee, will plunge his horns, and at last his head, driving up the earth, and soon making an excavation in the ground into which the water filters from amongst the grass, forming for him in a few moments a cool and comfortable bath, into which he plunges like a hog in his mire.