ATLANTIC COAST OF NOVA SCOTIA. G23 



Igneous action may produce still farther changes. The yellow 

 sand which results from the decay of granite is merely stained on 

 the surface by the ferruginous colouring matter, and a very slight 

 degree of heat is sufficient, by expelling the water of the iron rust, 

 to convert this yellow stain into a bright red. This change is super- 

 ficially produced by forest fires, and might readily occur when 

 decomposing granitic rocks have been subjected to the influence of 

 intensely heated or molten masses, with access of air or water. Red 

 sands and clays produced in this way, and washed into the sea, 

 become red sandstones and shales. Such red deposits are, however, 

 liable to still farther change. If long washed about in the sea, the 

 red coat is worn from the sands and added to the fine clays, so that 

 whitish sandstones may alternate with red shales. If vegetable or 

 animal matter is present, the changes of colour referred to in treating 

 of the marsh mud may take place, and dark-coloured or gray beds 

 may result, or greenish stripes and bands may appear in the mass of 

 red deposits. 



Clays and sands thus deposited may be hardened into i"ock by 

 pressure, by heat, or by cementing matter introduced by the per- 

 colation of mineral waters. 



It will thus be perceived, that from the granitic rocks it is possible 

 to deduce a variety of yellow, brown, and gray sandstones and shales, 

 quartzites, and slates. Many other rocks, however, beside granite 

 have been decomposed, especially to form the more modern deposits ; 

 hence more complicated results than those above stated have been 

 produced. Enough has, however, been said to show how much 

 derived deposits may differ in appearance from those which have 

 furnished their materials ; and also the mode in which the waste 

 of the older rocks has been disposed of. These facts also serve to 

 show the enormous waste or denudation which the older rocks 

 must have suffered in order to furnish the materials of the derived 

 formations, for example, of the Carboniferous beds. They farther 

 illustrate the connexion of red sandstones with periods of igneous 

 activity, and the prevalence of gray and dark-coloured sediments 

 at times when deposition has been slow and organic matter 

 abundant.* 



With respect to surface and industrial capabilities, the diflercnt 

 rocks occurring in this district present very various aspects. The 

 clay slate often has a regular undulating surface, and a considerable 

 depth of shingly or clay soil of fair quality, though usually deficient 



* See on tliis subject the author's Paper on " Tlie Colouring Matter of lied Sand- 

 i-tones," Jour, of Geol. Soc, and page \H suj'i'u- 



