78 



loped upon an enormous scale, and sometimes to form two distinct 

 chains of broken mountains, resting unconformably upon the primary 

 strata. On the south-eastern shores of the Murray Firth they gra- 

 dually thin off j and finally disappear near Cullen bay, in Banfshire. 



§ 3. On the general structure of Caithness. — After an account of 

 the external appearance of the county, the authors describe in great 

 detail two coast sections. The first, commencing with the old con- 

 glomerates of Port Skerry, which rest immediately upon the gra- 

 nite, exhibits the successive deposits in ascending order, and termi- 

 nates with the newer red-sandstone on the shores of the Pentland 

 Firth. The second section exhibited on the east coast, commences 

 with the newer red-sandstone, and passing through all the interme- 

 diate deposits, finally exposes the old conglomerate system in a part 

 of the coast between Borridale and the Ord. From a general review 

 of the phenomena exhibited in these two sections, as well as from 

 other details derived from the interior of the county, the authors 

 conclude that the secondary deposits may be divided into three great 

 natural groups : — 



1 . The old conglomerates, — which contain some subordinate masses 

 of red-sandstone, red marie, and calcareo-siliceous flagstone ; and 

 which, through the intervention of the red-sandstone, sometimes gra- 

 duate into the next system. 



2. A great formation, occupying all the lower regions of the county, 

 and composed of alternating beds of sandstone, siliceous and calcareo- 

 siliceous schist and flagstone, dark foliated bituminous limestone, 

 pyritous shale, &c. ; the siliceous beds giving the type to the lower 

 part of the formation, and the calcareo-bituminous beds to the interme- 

 diate part. This formation again becomes more siliceous and arena- 

 ceous in the upper portion, and so appears to graduate into the next 

 superior division. 



3. A great formation of red, brown, and variegated sandstone, which 

 composes lofty precipices on the south shores of the Pentland Firth. 

 It reappears on the other side of the Firth in the lofty red cliffs of the 

 Orkneys, and there also reposes upon a calcareo-bituminous schist. 



§ 4. Fossil fish of the secondary deposits of Caithness, #c. — These 

 seem to be contained almost exclusively in the calcareo-bituminous 

 schist, which is subordinate to the middle group of § 3. They do not 

 appear to be confined to any particular part of it, but were found in 

 various localities, some in the lowest and others in the highest part of 

 the series ; and in many places scales and imperfect impressions ex- 

 ist in the greatest abundance. Some imperfect specimens were ex- 

 amined during a preceding year by the Baron Cuvier, who found that 

 they all exhibited a pointed tail (with the rays exclusively on the lower 

 side, — as in the fish of the copper-slate of Thuringia), and notwith- 

 standing the great imperfection of the specimens, he concluded that 

 they were of the order Malacopterygii abdominales, and analogous to 

 the bony pike. Since that time much more perfect specimens have 

 been procured, which have been examined by Mr. Pentland ; who has 

 not only been enabled to confirm the conjectures of Baron Cuvier, 

 but has ascertained two new genera, each containing two species. 



