Mineralogy and Geology of Nova Scotia. 581 



same in appearance as those in the beds of many rivers, it is 

 probable that they were rolled by the action of water into their 

 present situation, where the external air being excluded by a 

 covering of earth, they were united by the crystallisation of a 

 portion of the siliceous earth they contained. 



A large collection of conglomerates, that is to say, of stones 

 composed of earth and broken stone cemented with quartz, 

 lime, oxides or carbonate of iron, &c, would go far towards 

 proving that many masses of rock were at some former period 

 collections of the debris of various kinds of stone thrown to- 

 gether promiscuously, which, petrified either by oxide of iron 

 from some contiguous mass of pyrites, or by the crystallisation 

 of a small portion of the silica or lime contained in the mass, 

 had since gone through certain changes (by means of an in- 

 ternal motion in the mass), which had made most of their 

 peculiar distinguishing marks disappear, and changed a con- 

 siderable portion of the mass into a homogeneous stone. 

 Fragments of felspar appear to be never affected by these 

 combinations any farther than taking the colour of oxides of 

 iron, and mica usually retains its natural appearance. The 

 cavities which abound in conglomerates at first are, by degrees, 

 occupied by a growth of transparent crystals, which are either 

 siliceous or calcareous, in proportion as these earths predo- 

 minate in the mass. It is most probable that the matter which 

 forms these crystals is dissolved in an aerial fluid. For it is 

 proved, by the appearance of those which are of several colours, 

 that they increase, like trees, by additional layers formed upon 

 their surfaces ; and it is inconceivable that the small quantity of 

 watery fluid borne by capillary attraction to the cavities could 

 be distributed over their surface in such a regular manner in 

 any other than a gaseous state. Many appearances in stones 

 render it probable that a part of these transparent erystallisa- 

 ations finally become opaque, and, by degrees, acquire the na- 

 ture of the rock in which they are embedded. Among the 

 fragments of porphyries and porphyroids which are generally 

 spread over the province, some specimens occur containing 

 small spherical nodules of reddish brown jasper, or a stone 

 approaching to jasper, which are generally solid ; but there 

 are some which have a cavity in the centre lined with pel- 

 lucid spar. Nodules containing similar cavities are some- 

 times found in the common fetid limestone, which are liable 

 to produce dangerous explosions when thrown into the fire. 



During the decomposition of pyrites, a portion of the rock 

 in which it is embedded is frequently decomposed. When this 

 rock holds a considerable proportion of silica, crystals appear 

 to form with great rapidity. I have seen, in the front of a perpen- 



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