

= ws = +. -1@0 
[Boox tL, 
336 DYNAMICAL GEOLOGY. 4 
the joints, the separated masses eradually assuming the form of 4 
rounded blocks like water-worn boulders. Other kinds decompose 
































































































































Fic. 86.—SPHEROIDAL WEATHERING oF DoteEriTr, NorTH QUEENSFERRY. 
to a depth of 30 or 40 feet, and can be dug out with a spade, as in 
Cornwall and Devon, where the kaolin from the rotted granite 1s 
largely extracted for pottery purposes. That what appears to be 
mere loose sand and clay is really rock decomposed in situ, is proved 

Fic. 87.—Basatr Dyker WEATHERING INTO SPHEROIDS. : 
by the quartz veins which ascend from the solid rock (a Fig. 88) into 
the friable part (>), and by the entire agreement in structure between 
the two portions. Jere and there kernels of still undecomposed 
