590 Mineralogy and Geology of Nova Scotia. 



most of our granite hills? that it was a mass of the debris 

 of granite mixed with rolled stones, which, since it was de- 

 posited in its present situation has been cemented by a portion 

 of its material, which had, probably, assumed a gaseous or 

 aerial state? If this were certainly demonstrated, it would ap- 

 pear very probable that our granite generally had, at an earlier 

 period, been in a similar state upon the surface, and that the 

 embedded pieces had been stones of another kind, which have 

 since become granite. I have seen so many facts which ren- 

 der it probable that quartz, felspar, and mica are, in some 

 cases, rapidly formed, that I think it by no means proved that 

 granite never contained any organic substance because they 

 are not now found in it. 



On slaty soils, the magnetic needle is very frequently turned 

 from its proper direction : the error does not often exceed 

 two or three degrees, but has been sometimes observed to 

 amount to ten. This magnetism is probably caused by iron 

 lately precipitated from a solution of vitriol in the state of an 

 imperfect oxide; for the bright pyrites is not magnetic, nor are 

 those ores in which the iron is in the state of a perfect oxide; 

 but the iron in vitriol is in the state of an imperfect oxide, like 

 the scales from the blacksmith's anvil. 



As peat earth decomposes vitriol, depositing the iron in the 

 state of a perfect oxide, the true direction of the needle may 

 generally be found by setting the compass in the middle of a 

 swamp: but this rule is not without exception; for I have seen 

 a swamp, more than twenty rods wide, in which the needle is 

 considerably affected. Small springs of chalybeate water are 

 always running into this swamp upon one side, and the lower, 

 of the hill ; on the opposite side are large masses of alum slate, 

 upon which the compass has been observed to change its di- 

 rection four degrees upon removing it 20 ft. In winter, the 

 true course may often be taken from a frozen lake. This 

 magnetism is sometimes observed on soils which rest on whin- 

 stone; out I have never observed it upon granite, I have, 

 however, observed a remarkable affection of the needle where 

 the suriace stones were all granite, there being a mass of that 

 rock half a mile to the northward. 



The bands of slate more frequently swell into lofty hills 

 than those of whinstone, and are therefore the worst situation 

 for roads, except the road runs in the direction of the hills. 

 The road through Preston to Chezzetcook follows the band of 

 slate upon which Halifax stands most of this distance. It 

 crosses so many high and steep hills, that it can never be made 

 a good road ; but, had it been bent a little southward at Lake 

 Loon, at the distance of three miles from the ferry, and, fol- 



