JONES — ON THE WEATHERING OF GRANITE 



305 



loose splinters and sand. In some instances, in the quarry and on 

 the neighbouring banks, this sand, or decomposed gTanite, has fallen 

 out and is scattered dowTi the slopes in thick beds, forming the 

 "granit pourri" of continental geologists. This substance covers 



Lign. 6.— Joints in Granite, Eastern Face of Old Quarry, below Haj'tor. 



vast areas in some granitic regions, and is used for the pui'poses to 

 which sand and gTavel are applied in tertiary and alluvial districts. 

 In this old quarry the horizontal joints of the gTanite are less 

 widened than are the perpendicular joints by atmospheric causes act- 

 ing on their bounding planes. 



In another quarry, on still low^er ground, and but little fui'ther 

 to the west (from which the granite was chiefly obtained for 

 building London Bridge), the vertical and horizontal joints are 



Lign. 7.— Eastern Face of New Quarry, Haytor. 



again well seen on the smooth sides of the pit. Fig. 7 shows 

 the eastern face. Here the joints are all closed, and their sides 

 are nearly unaffected by change, except some alteration in the 

 colour of the stone along their lines. At one spot, shown in 



