138 DISINTEGRATION &c. OF ROCKS. 
around the moor for fuel. Where this peat, or the 
old soil of furze-brakes constitutes the land of en- 
closures, a free admixture of lime seems not only 
advisable but requisite for the procurance of crops, 
as I have noticed elsewhere. These peat beds when 
cut or disturbed are reported to vegetate anew. 
In this class of formations, also may be ranked 
the soils and deposits formed from the solution, 
disintegration, decomposition and separation of the 
looser fragments of rocks by existing causes, chiefly 
atmospheric. ‘The granite of Dartmoor where it 
contains a superabundance of felspar, gradually 
decomposes, and varies in softness down to “ porce- 
lain earth” which may be cut with a spade. Many 
parts of the moor present extensive beds of this 
substance, and one found of late years near Shaugh 
employs at present a great number of men in the 
process of casking it for exportation. 
Dolomite is susceptible of a similar description of 
decomposition or softening, as I have noticed at 
Yealmpton both in large quantities and in mere 
superficial alteration of the stone by the action I 
believe of the water of the soil and air. 
The variegated sort of trapp is from its compara- 
tively loose texture liable to disintegration from the 
to the above mass which has a horse-shoe for its nucleus. On the 
northern coast of Cornwall so greatly exposed to the fury of the 
winds, vast quantities of calcareous sand are continually carried 
to the land, and form districts of hillocks of this material. In 
some spots it becomes consolidated by the infiltration of ferrugi- 
nous particles derived it is presumed from the adjacent ancient 
rocks, and so great is its density as to be even used as a building 
stone. “The infiltration of water thus impregnated, Dr. Paris 
“ observes, is a common and extensive cause of lapidification ; at 
«“ Pendean Cove, granitic sand is gradually hardening into a breccia 
“by this process ; and in the Island of St. Mary, Dr. Boase has 
“noticed granitic sand becoming indurated by the slow action of 
“ water impregnated with iron.” see p. 71, Mantell ut supra. 
