On the Strata of the Western Coast and Islands. 315 



Although no traces of the Upper Oolite or the Neocomian forma- 

 tions have as yet been detected in the Western Highlands, yet it 

 is argued that when we consider how enormous has been the amount 

 of denudation, and how singular the accidents to which all the ex- 

 isting relics of the Secondary period have owed their escape from 

 total destruction, we cannot but regard it as a most rash and 

 unwarrantable inference to conclude that no deposits belonging to 

 those periods were ever accumulated within the district under consi- 

 deration. 



The Carboniferous strata of the Western Highlands have been 

 detected at but a single locality, and even there, being exposed in 

 a series of shore-reefs that are only occasionally well displayed, 

 can only be studied under favourable conditions of tide and wind. 

 They consist of sandstones and shales with thin coaly seams ; and 

 their age is placed beyond question by the discovery in them of 

 many well-known plants of the coal-measures, including species of 

 Lepidodendron, Oalamites, Sigillaria, and Stigmaria. 



The Poikilitic strata consist of conglomerates and breccias at the 

 base, graduating upwards into red marls and variegated sandstone, 

 which contain concretionary limestones and occasional bands of 

 gypsum. These strata have not as yet, like their equivalents in 

 the Eastern Highlands (the Reptiliferous Sandstone of Elgin and 

 the Stotfield rock), yielded any vertebrate remains. They were 

 evidently deposited under similar conditions with the beds of the 

 same age in England, and are not improbably of lacustrine origin. 



The Jurassic series presents many features of very great interest. 

 The Infralias is better developed than is perhaps the case in any 

 part of the British Islands ; and in the district of Applecross a series 

 of estuarine beds containing thin coal-seams is found to be inter- 

 calated with the marine strata. 



The Lower Lias, in its southern exposures, presents the most 

 striking agreement with the equivalent strata in England, but 

 when traced northwards exhibits evidence of having been deposited 

 under more littoral conditions : the lower division (Lias a, Quen- 

 stedt) is represented by a great thickness of strata ; while the upper 

 (Lias /3) is absent or rudimentary. The Middle Lias is grandly de- 

 veloped, and consists of a lower argillaceous member and an upper 

 arenaceous one, the united thickness of which is not less than 

 500 feet. The Upper Lias singularly resembles, in the succession 

 of its beds and its palaeontological characters, the same formation 

 in England. The Inferior Oolite is formed by series of strata 

 varying greatly in character within short distances, and betraying 

 sufficient signs of having been accumulated under shallow-water 

 conditions. Above the Inferior Oolite we find a grand series of 

 estuarine strata, partly arenaceous and partly calcareo- argillaceous ; 

 and this is in turn covered conformably by an unknown thickness 

 of blue clays with marine fossils of Middle Oxfordian age. At the 

 very lowest estimate, the Jurassic series of the Western Highlands 

 could not have had a thickness of less than 3000 feet ! 



The Cretaceous strata of the Western Highlands, though of no 

 great thickness, are of surpassing interest. They consist of two 



