ON THE DESTRUCTION OF ROCKS. 265 



is intersected. In many places in Aberdecnshire, 

 where the whole mass of granite has decomposed 

 together, in the manner hereafter described, the per- 

 manence of these veins produces very remarkable 

 appearances. While all the surrounding rock is 

 converted into clay and gravel, the veins remain en- 

 tire, and may be removed in solid pieces of consi- 

 derable dimensions resembling slates. 



The oval or oblong cavities which are occasionally 

 seen in many of the stratified rocks, and which some- 

 times strongly resemble the human footstep, seem to 

 belong to the same cause. A most remarkable in- 

 stance of these is seen at the entrance of Loch 

 Craignish on the west coast of Scotland, where a 

 double and alternating row is prolonged for some 

 distance, in a variety of chlorite schist, in a manner 

 so accurate as to represent a series of the foot-prints 

 of an individual. In limestone, similar marks are 

 familiar, and they also occur in clay slate, in 

 Galloway. 



The decomposition of the secondary sandstones is 

 often attended by a great number of extraordinary 

 appearances besides that above named ; the conse- 

 quences of internal structures which could not be 

 suspected, and of which the fracture of the unaltered 

 rock gives no indications. The spheroids of Egg, 

 often reaching to three feet in diameter, are disco- 

 vered only by the crumbling of the including portions ; 

 and, in Arran, a minute structure of the same nature 

 is found, covering the surfaces which are exposed to 

 the wash of the sea. On the shores of Fife, and 

 elsewhere, the same process detects the existence of 

 small cylindrical bodies placed in parallel order at 

 right angles to the planes of the beds ; as if colonies 



