SURFACE. 27 



fire limit, are yet very nearly level, having been protected 

 from the action of the elements by the lava and half- 

 molten rocks with which they are covered. 



Portions of the second plain are also yet found which 

 are not broken by ravines. These were probably very 

 level areas of the original ocean-bed, which in the up- 

 heaval were lifted so horizontally that the rains found no 

 inclination, and were absorbed by the porous soil before 

 having time to make one. Even when they occur, these 

 level plains are very limited in extent, and generally have 

 one, or many, depressions in their surface of greater or 

 less extent, which are lakes after rains. 



On this kind of prairie are found the curious depres- 

 sions called ' buffalo wallow.' These are formed in the 

 following manner : A heavy rainfall deluges the hard and 

 level prairie. The water is soon absorbed by the thirsty 

 soil, or licked up by the hot sun-rays; a portion of the 

 soil, a little more moist than that adjoining, opens in cracks, 

 such as can be seen in any ordinary dried-up mud hole. 

 Another hard rain comes : these cracks are filled up by 

 earth washed from their edges, which, packed more 

 tightly, and retaining moisture longer than before, cracks 

 again wider in drying. This process is repeated again arid 

 again, until quite a depression is made into the soil, which 

 is now so tightly packed as to retain water for a consider- 

 able time. When the buffalo is shedding his coat in the 

 spring, he is constantly endeavouring to get rid of the 

 superfluous hair, and, in the absence of trees against which 

 to rub, he is frequently rolling and rubbing himself on 

 the ground. These small water-holes are his especial 

 delight. He throws himself into them with the greatest 

 satisfaction, rolling and plunging, and rounding out the 

 hole until it is of a size to fit comfortably his huge pro- 

 portions. Sometimes the prairie will be dotted for a mile 

 with these holes, which are generally oval in shape, five 

 to ten feet long, three to five broad, and from six inches 

 to two feet in depth. 



