and some other Stratified Deposits in the North of Scotland. 301 



atmosphere; and so much indeed is that mineral disseminated throughout 

 this district^ that the shales might generally be termed " pyritiferous." 



Although 14 or 15 slight dislocations are connected with the pit now in 

 use, the present level was driven nearly 900 yards before the great fault was 

 met with, which limits the coal-field upon the West, where lower beds con- 

 taining nodules of blue limestone with septaria, are brought up near the 

 salmon cruives. It is probable that from this place have been derived those 

 boulders which are seen at the mouth of the river Brora, and which so 

 resemble the cement stones of the alum shale at Whitby. Some of these faults 

 are occupied by a white quartzose, and highly indurated sandstone, having a 

 conchoidal fracture. Sinkings subsequently made below the working level, 

 passed through beds of bituminous shale for upwards of 90 feet, when sandy 

 clays of a loose structure stopped the works by occasioning a great influx of 

 water ; and therefore the whole depth of the sand and shale below the coal 

 has never been ascertained. 



The beds in contact with the granitic range are about one mile and a half 

 distant from the coal-field, if the application of this term be restricted to that 

 area in which the mineral has been discovered : indeed all attempts to work 

 coal resting upon granite, would be impracticable, on account of the dismem- 

 berment of the strata which invariably accompanies such junctions. 



For an analytical view of the chemical changes in the various lignites, from 

 those of the highest formations down to the more perfectly bituminized sub- 

 stances similar to this under consideration, I refer to the Works of Dr. MacCul- 

 loch. With respect to the Brora coal, the purer part of it differs in no respect 

 from the coal of the carboniferous series when subjected to chemical analysis ; 

 but it off'ers a mineralogical distinction upon being pulverized, assuming like 

 all lignites a red ferruginous tinge, and thus differing from the true coal 

 which works into a black powder *. The laminae between the seams of the 

 latter are generally coated with pure carbonaceous matter, whilst those in the 

 Brora coal are occupied by bituminous shale. It may be considered one of 

 the last links between lignites and true coal, approaching very nearly in cha- 

 racter to jet, though less tenacious than that mineral; and when burnt, only 

 slightly exhaling the vegetable odour so peculiar to all imperfectly bitumi- 

 nized substances. The fossil remains of shells and plants prove the Brora 



* The same test does not strictly apply to all specimens of the coal, either at Brora or on the 

 east coast of Yorkshire, which, although it occupies the geological place of lignite, is in some places 

 not to be distinguished mineralogically from ordinary coal. 



