42 NATURE STUDY. 



verdure throughout the extensive area of the great Appa- 

 lachian mountain system. 



On its northerly side, the hill is already well rounded to 

 a comparatively gentle slope, probably the result of glacial 

 action in the ice age, long ago, and here trees, shrubs and 

 coarse grasses grow well up toward the naked summit. 

 The southerly side is a sheer precipice, about 90 feet in 

 height and some 120 feet in length. Scattered over the 

 plain, for several rods from the base, are rough blocks of 

 stone, some of large size, which have fallen from the preci- 

 pice above. These were loosened from the ragged edge of 

 the great rock by the action of frost and heat and rain and 

 snow, falling, perhaps, at the rate of one in a century, pos- 

 sibly of one in a thousand years. 



At the base, smaller fragments have accumulated unti 

 they form a slope at what is known as the angle of repose, 

 reaching up one-third of the height of the precipice, and 

 covered with shrubs and small trees. Some day, thou- 

 sands of years from now, the top of the precipice and this 

 slope will meet, and there will then be a rounded hill, cov- 

 ered with grass and shrubs and trees, like other hills in 

 the neighborhood that were finished earlier. 



Meanwhile, on and around the summit other processes 

 are going forward. At the very top, the otherwise naked 

 rock is covered with lichens, which, as they die, are 

 washed by the rains into depressions a few feet below. 

 Perhaps, too. they help the cold of winter and the heat of 

 summer in the work of breaking up the rock surface into 

 tiny fragments that are also washed down into the depres- 

 sions, where enough soil is thus formed to support beds 

 of moss. This moss, growing, dying and decaying, year 

 after year, further increases the soil, which in time fills 

 the depressions, after which the surplus accumulation is 

 washed still farther down by the rains and melting snows. 



At this next lower level, sedges, coarse grasses and ferns 



