JONES — ON TUK VVEATIIEKINO OF GRANITE. 
811 
sometimes scarcely coherent, and, on exposure to the weather, soon 
falling away. Along the belt where the basins exist, the granite is 
for the most part more liable to decomposition than at the harder 
and more crystalline tors. This is shown by the many rounded tors, 
and every roadside-cutting shows the rapidity of the decay. The 
division of the granite into tabular sheets of rock of irregular thick- 
ness, causing the appearance of stratification, is common to all the 
granite of this district. In irregularities on the surface of the 
granite, and in hollows, very probably in many cases caused by the 
nodules above noticed, water lodges on and penetrates into the 
porous granite, and the decay thus commenced will gradually enlarge 
the cavity to a basin. During the inclement part of the year these 
basins are full of water, that during part of the time often rapidly 
alternates with ice. When the warm weather comes on, the water 
evaporates, and the basins are dried up ; from the frequent showers 
there is, then, a constant change between the rock being saturated 
with wet and it being warm and dry. The gradual action of the 
water is very perceptible ; when it has evaporated, the stone up to 
thCj, water-Hne is left a Ughter shade than the adjoining rock; the 
felspar-crystals instead of presenting their usual appearance, are dull 
and full of minute cracks, and appear as if about to fall into small 
fragments similar to those found in the basins ; the action of the 
water is evident to the eye though not easily described. An un- 
broken face of granite resists the weather more powerfully than the 
rock does when it is broken or penetrated ; in those cases the water 
soaks into the granite, and thus renders it more easily acted upon by 
the alternations of heat and cold, wet and dryness. Such action 
when once commenced will continue until checked by the unbroken 
face of a parting wliich will limit the extension either perpendicularly 
or horizontally. The tabular formation of the granite is probably 
the cause of the frequent occurrence of the basins with flat bottoms. 
The gradual decay thus acting from a centre will cause the nearly 
circular and oval forms that so many of the basins present, the 
variation from that shape being probably caused by a difference in 
the structure of the granite. The eye will in a short period dis- 
criminate between the tors where basins would probably be found or 
not. Firstly, where it is the character of the tor to have the per- 
