Parr IL Secr. ii.§1.] WEATHERING. — Sey 
granite may be seen (as at cc in Fig. 89), surrounded by thoroughly 
decayed material, and, like the solid cores of basalt, above mentioned, 
presenting a deceptive resemblance to some accumulation of trans- 

or Cuber Ce] are 
— cece ee 
Fic. 88.—DEcoMPOSITION OF GRANITE. Fic. 89.—DECOMPOSITION OF GRANITE, 
a, Solid granite; 6, decomposed granite ; a, solid granite; 6, decomposed 
c, vegetable soil. granite; cc, kernels of still unde- 
composed granite. 
ported materials. Owing to its numerous joints, granite oceasionally 
weathers into forms that resemble ruined walls. Large slabs, each 
defined by joint planes, weather out one above another like tiers of 
masonry (Fig. 90). As these become surrounded and loosened by dis- 
integration they slip off and expose lower parts of the rock to the same 
influences. Here and there a separate block becomes so poised that 
it may be readily moved to and fro by the hand, as in the so-called 
“rocking-stones” of granitic districts. The disintegration being 
likewise liable to considerable local differences, some portions of the 

Vie. 90.—WEATHERING OF GRANITE ALONG ITS JOINTS (B.). 
blocks are weathered into cavities often with a singularly artificial 
appearance, as in the “rock basins” of the south-west of England 
Fig. 91). 
Po a influence of weathering many of the most familiar minor 
contours of the land may be traced. So characteristic are these 
forms for particular kinds of rock, that they serve as a means of 
recognizing them even from a distance. (Book VIL.) 
In countries which have not been under water for a vast lapse of 
time, and where consequently the superficial rocks have been con- 
tinuously exposed to subaerial disintegration, thick accumulations of 
“rotted rock” are found on the surface. The extent of this change is 
sometimes impressively marked in areas of calcareous rocks. Lime- 
stone being mostly soluble, its surface is continually dissolved by rain, 
while the insoluble portions remain behind as a slowly increasing 
deposit. In regions which, possessing the necessary conditions of 
climate, have been for a long period unsubmerged, tracts of lime- 
stone, unprotected by glacial or other accumulations, are found to 
be covered particularly with a red loam or earth. This character- 
3 Z 
