THE WEATHEEING OP BOOKS 161 



the one underlying principle of transformation from the un- 

 stable toward that which is to-day more stable. Nothing is 

 lost or wasted: It is a change which began with the beginning 

 of matter; which will end only with the blotting out of matter 

 itself. There are no traces of a beginning^ there is no prospect 

 of an end. 



I. THE PEINCIPLES INVOLVED IN EOCK- 



WBATHERING 



The processes involved in this readjustment from unstable 

 to stable compounds, as above outlined, and of incidental soil 

 formation, are in part physical and in part chemical in their 

 nature; they operate under every-varying conditions, and 

 through proc3Sses at times simple, or again complex. What 

 these processes are, and how they operate, it must be our purpose 

 to now consider. 



It may be said at the outset, that whatever the forces en- 

 gaged, they are, with a few isolated exceptions, superficial, — 

 they work from without downwards. However much they may 

 have accomplished since the first rock masses appeared above 

 the primeval ocean, in no ease can the actual amount of debris 

 in situ have formed at one time more than a scarcely appreciable 

 film, geologically speaking, over the underlying and unchanged 

 material. The decomposing forces early lose their active prin- 

 ciples and become quite inert at depths comparatively insignifi- 

 cant. It is only where through erosion the results of the disinte- 

 gration are gradually removed, that the processes have gone on 

 to such an extent as to perhaps quite obliterate thousands of feet 

 of strata or of massive rock, and furnished the necessary debris 

 for the vast thicknesses of sandstone, shale, and slate which 

 characterize the more modern horizons. In certain isolated cases, 

 it is true, ascending steam and heated waters, arising from depths 

 unknown, have been instrumental in promoting decomposition, 

 as is well illustrated in the areas of decomposed rhyolites in the 

 Yellowstone National Park. Nevertheless, it is to the slow process 

 of superficial weathering that we owe a very large share of the 

 apparent rock decomposition and incidental soil formation.^ 



^ The term weathering , as here usecl, is applied only to those superj&cial 

 changes in a rock mass brought about through atmospheric agencies, and 

 resulting in a more or less complete destruction of the rock as a geological 



