134 Rev. A. Sedgwick cmd Mr. Murchison on Deposits contained between 



tlaiik of the headland there is much confusion ; the thin beds of the former being contorted and 

 brought up by a fault against the edges of tlie latter. On the southern shore of the Pentland 

 Firtii, between Dunnet and Duncansby Heads, tlie various projections consist either of the 

 upper red sandstone, or of the beds which pass into it ; whilst the indentations of the coast 

 expose the flagstone beneath them. It is, however, essential to our purpose to describe in 

 some detail a part of the coast east of Barrogill Castle, where the strata of an intermediate 

 character between the flagstones and the newer sandstone are more particularly developed ; 

 since a great portion of these beds, as has before been stated, are obscured by blown sand in the 

 section of Dunnet Bay. 



Near Barrogill Castle, the lowest beds visible are calcareous and micaceous schists of a bluish 

 colour; and in one place they enclose a bed of brown schist so highly bituminous, as to be occa- 

 sionally used for fuel (dip E.N.E. 20°). The ascending series from these flag beds consists of 

 bluish and greyish siliceous schists, sometimes slightly calcareous, alternating with shivery, thin 

 folia of sandy shale. These are, in their turn, surmounted by tabular, calcareous sandstones asso- 

 ciated with highly pyritiferous beds, much indurated, and of a fissile structure; and, continuing 

 in the same order, the beds thicken, acquire a honeycombed aspect, and have a bright yellow 

 exterior, alternating with green-coloured shale. Some of the siliceous beds take a lozenge. shaped 

 concretional form, splitting into regular septaria, and are of exceeding hardness. The beds just 

 described occupy a shelving shore ; but they afterwards rise into a cliff towards the east, of thirty 

 or forty feet in height, which is cut into by straight-lined fissures, forming caverns and creeks. 

 Here the flagstones are partially covered with blotches of thick black bitumen, soft to the touch, 

 and as adhesive as tar*. Some of the lamellar beds are so highly calcareous as to be burnt for 

 lime ; and with these are associated innumerable scales and other portions of fish. 



The above system of beds runs out to form the base of St. John's Head, and their total thick- 

 ness cannot be estimated at less than from three to four hundred feet. To the S.E. of that pro- 

 montory, the coast is indented in the form of a small round bay called Scotland's Haven, on the 

 west of which the beds above described, dipping to the east, pass under the upper red sandstone, 

 which shows itself on the opposite side of the bay under its most decided characters. Towards 

 Cannisby, the red sandstone becomes nearly horizontal, and is spread over a mile of low shore, 

 the cliffs being entirely occupied by vast masses of modern detritus. Previously to reaching Can- 

 nisby, a fault suddenly brings up the flag series against the newer sandstone, which again rises to 

 form the cliff at Cannisby; from whence to John-o-Groats the shore is low, and is only occa- 

 sionally occupied by reefs of the upper sandstone, the beds of which at the latter place are fine- 

 grained, and in some places nearly compact. A slight north-easterly dip continues to that eleva- 

 tion of the coast called Duncansby Head, where there is a great disturbance in the strata, the 

 upper red sandstone being suddenly thrown up at 70"°, dipping W.N.W. By this fault the lower 

 beds of flagstone are brought to the summit of the cliff, which is fissured in many directions by 

 deep, straight, perpendicular gullies. Some of these cut off from the headland great masses of 

 the horizontal strata, which in the progress of degradation look like ruined buildings; whilst 

 others cleave their way through a clitt" more than 250 feet in height, and range towards the in- 

 terior of the country. These pha^nomena are of no ordinary grandeur, and they derive a local 

 interest from being connected with the extreme north-eastern promontory of Scotland. 



* In the slaty schists of Seefeld in the Tyrol, there is such an abundance of a similar bitumen, 

 that it is largely extracted for medicinal purposes : a notice of this deposit, and the fossil fish 

 contained in it, has been given by one of the authors of this memoir. See Phil. Mag. July, 1829. 



