Geological Society. 223 



§ 2. Range of the old-red-conglomerates through Caithness, and on 

 the shores of the Murray Firth, #c. — These rocks are stated to appear 

 in several unconnected masses on the north coast, between Cape 

 Wrath and Port Skerry ; and from the latter place they range into 

 the interior, and rise into a mountain -chain (the highest parts reach- 

 ing the elevation of 3500 feet), which is continued to the granite of 

 the Old of Caithness. Their range parallel to the shores of the Murray 

 Firth, is also given with many details. They are slated to be deve- 

 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 Banfshrre. 



§ 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 



