PRINCIPLES OF R O CK 1 1 V;. I THE RING 855 



infrequently charged to the point of turbidity with the fine silt- 

 like detritus ground from the ledges and in part from the bowl- 

 ders themselves. This feature has been so frequently noted in 

 geological text-books, as to need no farther mention here. 



id) Action of plants and animals. — Both plants and animals 

 aid to some extent in the work of rock degeneration. 



The lowest forms of plant life, the lichens and mosses grow- 

 ing upon the hard, bare face of rocky ledges, send their minute 

 rootlets downward into every crack and crevice, seeking not 

 merely foothold but food as well. 



Slight as is the action it aids in disintegration. The plants 

 die, and others grow upon their ruins. There accumulates thus, 

 it may be with extreme slowness, a thin film of humus, which 

 serves not merely to retain the moisture of rains but also to 

 bring the rock under the mfluence of chemical action. As time 

 goes on, sufficient soil gathers for other, larger and higher types 

 of life, which exert still more potent influences. It may be the 

 rock is in a jointed condition. Into these joints each herb, 

 shrub, or sapling pushes down its roots, which in simple virtue 

 of their gain in bulk, day by da}-, serve to enlarge the rifts and 

 furnish thereby more ready access for water, and the wash of 

 rains to still further augment disintegration. This phase of root 

 action is often well shown in walls of ancient masonry, either of 

 brick or stone, where they greatly accelerate the usual rate of 

 destruction. The depth to which such roots may penetrate has 

 often been noted,' varying, as is to be expected with the nature 

 of the soil. In the limestone caverns of the southern states the 

 writer has often noted the number of long thread-like rootlets 

 which have found their way through rifts in the rocky roof, so 

 fine as to be almost imperceptible. In this, as in others of 

 nature's processes, we must remember that nothing is done in 

 haste. With boundless time, and resources without limit. Dame 

 Nature works out her results at her own time and by her own 

 methods. 



■ Aughey has found roots of the buffalo berry {Sheperdia argop/iyHa) penetrating 

 the loess soils of Nebraska to the depth of fifty feet. 



