592 Mineralogy and Geology of Nova Scotia. 



slate, but not easily. It has formerly been used in Halifax for 

 hearthstones and tombstones. Small veins of it are almost in- 

 variably attached to those masses of whinstone which are of a 

 good quality for building stone. 



The reddish brown porphyries and porphyroids, which, in 

 small fragments, are generally scattered over nearly the whole 

 province, most plentifully in clayey soils, were probably ori- 

 ginally all conglomerates, formed from fragments of stones 

 of various kinds thrown promiscuously together, which have, 

 by means of an internal motion, so mingled the materials of 

 which they were composed, that they have now become a 

 homogeneous mass, with the exception of the felspar and 

 quartz. The sandstones appear generally to differ little from 

 the sandy soil which covers them. If the one contains rolled 

 stones, they are found of the same kind, and in the same pro- 

 portion, in the other; and they always alternate with about an 

 equal proportion of a hard .fine-grained stone, as sand, upon 

 digging deeply into it, is found to do with claj'. The three 

 components of granite never show any tendency to unite as a 

 homogeneous mass; it is therefore probable that our granite 

 resembles that of former periods : yet is there good reason 

 to believe that it has been, on the surface at least, in a state ol 

 disintegration, and also that it has a tendency to penetrate and 

 change to granite some portion of those rocks which are in 

 contact with it ; mica, during this process, always preceding 

 the quartz and felspar. 



The common slate has clefts which admit some air for many 

 feet in depth ; and it appears to have suffered considerable 

 changes, caused by the decomposition and growth of pyrites, 

 and also of a portion of the stone: for, in breaking some kinds 

 of slate, small cavities are found containing an earth differing 

 little from magnesia, and many fissures, filled with the same 

 earth, united with a little oxide of iron, and assuming a degree 

 of hardness approaching to stony; and in calcareous vitriolic 

 slate, which is in a state of decay, thin veins of selenite may be 

 found, so soft that it may be ground with the teeth when first 

 taken from the stone: indications that, during the decomposi- 

 tion of pyrites, a portion of the stone in which it is enclosed 

 is also decomposed. 



The whinstone also bears strong marks of having once been 

 in a broken decayed state, and of having again become a solid 

 rock. While these, changes have been going on near the sur- 

 face, it is probable that metallic ores, and other homogeneous 

 minerals, have, by degrees, been collected in the deeper cavities 

 and fissures of rocks which contained a small proportion of 

 them diffused through their mass. Sulphur, so generally con- 



