584 Mineralogy and Geology of Nova Scotia. 



future generations ; and that it must have been as valuable to 

 the aboriginal inhabitants as the more fertile districts, during 

 that unknown number of ages which preceded the (to them) 

 fatal period, when, "their times being fulfilled," that power 

 was guided to the American shores, which " devoureth, break- 

 eth in pieces, and stampeth the residue with its feet." 



Upon turning our attention to the slates, we shall, with 

 the little knowledge we possess, be able to perceive that they 

 are useful to man, and that they have not been " created in 

 vain." 



To render the purpose for which the specimens of this stone 

 are collected intelligible to those who have paid no attention 

 to chemistry, it is necessary to observe, that all slate which is 

 covered with a coating of rust (technically called brown or 

 yellow oxide of iron) either contains, or has contained, pyrites, 

 a mineral which has a metallic lustre, and which varies in co- 

 lour from white to yellow ; that the pyrites in the common 

 slate is principally composed of sulphur and iron ; that, 

 with the exception of the species called marcasites, which is 

 crystallised in regular figures, it is always decomposed by ex- 

 posing it to the action of the air for a few years ; the sulphur, 

 by attracting oxygen from the atmospheric air, becoming sul- 

 phuric acid, dissolving the iron, and forming the salt called 

 sulphate of iron (the common green copperas of commerce); 

 the pyrites, during the process, losing its lustre, and either 

 falling to a powder, or becoming a soft blackish stone. 



This salt, dissolved by the water absorbed by the rock, 

 sometimes forms chalybeate springs, but more frequently rises 

 in small fissures to the surface of the rock by the power of 

 capillary attraction, where it forms those white lines which 

 may always be observed upon slate rocks after a few fair days 

 in summer. 



When a solution of copperas is exposed to the air, it is soon 

 decomposed by new combinations. This decomposition is 

 accelerated by its coming in contact with vegetable mould or 

 peat earth. The oxide of iron separates in a light bulky state, 

 giving the water a thick oily appearance and ochraceous colour; 

 a state in which it may often be observed in ditches on the 

 peninsula. This substance, on poor soils, soon hardens, en- 

 crusting the stones, and often cementing the gravel and form- 

 ing large masses of conglomerate rock, such as composes the 

 bank on the south side of the Governor's Farm, and in several 

 places on the shore of Dartmouth. Even on fertile soils, frag- 

 ments of slate may be found, which have doubled their bulk 

 by petrifying a portion of the contiguous soil. 



Slate stones, therefore, which have a strong brown crust. 



