S08 Mr. MuRCHisoN on the Coal-field of Brora in Sulherlandshire, 



is recumbent with a highly inclined dip upon a granitic rock, very similar (o 

 that of the Ord of Caithness. Near this junction, beds of dark coloured mica- 

 ceous shale, only visible at low water, dip away from the coast, restinij uncon- 

 formably upon the edges of the sandstone of the red conglomerate. These 

 shales extend about three quarters of a mile from N. to S., and, at low ebbs, 

 are developed through an equal space from W. to E. They are remarkably 

 curved in one situation, where the softer portions having been washed out, 

 the harder shales with limestone rise one above the other, and thus present 

 the appearance of seats in an ancient tlieatre 



The laminated beds contain a compact blue argillaceous limestone marked 

 by veins of carbonate of lime ; and nodules identical with the cement stones of 

 the alum shale are not unfrequent. The fossil shells which I procured during 

 one ebb of the tide are those of the lias ; V\z. gryphaea gigantea, G. incurva ; 

 ostreae, belemnites, ammonites, &c. 



These beds are cut off upon the south by lofty cliffs, the insulated and 

 broken peaks of which continue to distinguish this bold coast on both sides 

 of Cromarty Bay. These cliffs are composed of various primitive rocks^ much 

 elevated and contorted, traversed by numerous veins of the granitic rock. 

 (See PI. XXXI. fig. 3.) 



Passing to the south of Cromarty Bay, the coast is still chiefly occupied by 

 cliffs of the granitic rock ; but the black shales and blue limestone beds re- 

 appear in Ethie Bay, where a fine-grained whitish variety of the red conglo- 

 merate composing that large peninsula of Ross-shire, called the "Black Isle," 

 is elevated into lofty hills. Many of these beds at Ethie, although principally 

 composed of granitic detritus, contain much calcareous matter : others, it must 

 be stated, strongly resemble the old red sandstone of South Wales, particularly 

 in having a subordinate bed of red limestone which is very similar to the corn- 

 stone ; and the whole suite is interspersed with much mica, chlorite, and indis- 

 tinct corbonaceous markings. The shale beds on the shore are clearly a portion 

 of the same series as those beyond the North Sutor, from which they are dis- 

 tant about eight miles. They dip away from the coast at about an angle of 

 30°; and, with the exception of some partial dislocations and contortions, they 



slight ground for presuming that the sandstone of these districts may be the equivalent of the 

 newer red sandstone which is so uniformly distinguished in England and elsewhere by the rich- 

 ness of its .soil ; the sandy tracts of the old red being usually marked by their sterility. The stone 

 of the Red Castle and Tarradale quarries strongly resembles some beds of the new red sandstone 

 near Bristol ; and sulphate of strontian, a mineral characteristic of that formation, is found at 

 Clachnacarrich near Inverness: which place, although to the South of the Murray Firth, may 

 still be considered within the range of the red conglomerate. 



