Dr. Mac Culloch m the Granite 'Tors of Cornwall, 73 



They are of various depths, and they may be sometimes observed to 

 communicate with each other. Their artificial appearance was suf- 

 ficient to convince of the truth of his system regarding them, this 

 strenuous supporter of a worship which must on his hypothesis have 

 required a priesthood sufficient to exclude all other population, if 

 every rounded cavity which the granite exhibits was a pool of lus- 

 tration. 



Their true origin is easily traced by inspecting the rocks them- 

 selves. On examining the excavations, they will always be found 

 to contain distinct grains of quartz and fragments of the other con- 

 stituent parts of the granite. A small force is sufficient to detach 

 from the sides of these cavities additional fragments, showing that a 

 process of decomposition is still going on under favourable cir- 

 cumstances. These circumstances are the presence of water, or the 

 alternate action of air and water. If a drop of water can make an 

 effectual lodgment on a surface of this granite, a small cavity Is sooner 

 or later produced. This insensibly enlarges as It becomes capable of 

 holding more water, and the sides as they continue to waste, neces- 

 sarily retain an even and rounded concavity, on account of the uni- 

 form texture of the granite. In time, the accumulated gravel is 

 blown away by the winds, although In the deeper hollows it may 

 often be found forming considerable accumulations. 



The same solubility of granite In water, (to speak generally) is the 

 cause of that wasting of the surface which these rocks undergo, and 

 to which I have before attributed the enlargement of the vacuities at 

 the surfaces of contact, and the separation of the prisms into detached 

 masses. 



We need not hesitate in admitting the solution of granite in water 

 to an extent capable of producing this effect of disintegration, since we 

 know that silex is soluble in that fluid by natural means, however we 



Vol. II. K 



