688 J. W. JTJDD ON THE SECONDARY ROCKS OE SCOTLAND. 



passing into calcarous grits, and some of the clays becoming true 

 marls. The "beds are frequently found to be traversed in all direc- 

 tions by innumerable veins of Calcspar. 



That the limestones are of chemical and not organic origin is 

 evident both in the case of the beds in the Western Highlands and 

 in that of the equivalent " cherty-rock of Stotfield," with which they 

 so closely agree in character. From a study of all the features of 

 these Poikilitic strata of the Highlands, I am inclined to accept the 

 suggestion first made by Mr. Godwin- Austen, and afterwards sup- 

 ported by Prof. Ramsay, with regard to their English equivalents — 

 namely, that they have been accumulated in inland lakes and not 

 in the open ocean. In the Poikilitic strata of the island of Inch 

 Kenneth some irregular beds and veins of gypsum occur ; and these, 

 though of no considerable thickness or importance, constitute another 

 point of resemblance between the Highland strata and their equi- 

 valents in the southern part of the kingdom. Beds of rock-salt, it 

 is true, do not occur in them ; but in almost every other respect 

 the resemblance between the Poikilitic strata in the northern and 

 southern areas of Britain is of the most marked character. 



The Poikilitic Series of the Western Highlands varies greatly in 

 the thickness and order of succession of its beds. While at Grui- 

 nard Bay it certainly exceeds 1000 feet, in Baasay it is probably 

 less than one half that thickness, and at Lussa}^ in Skye, it is re- 

 duced to a few feet only. At Bu-Geur, in Sleat, the formation 

 shows signs of regaining somewhat of its thickness and importance, 

 which characters it certainly retains in Ardnamurchan and some 

 points in Mull, while in Morvern it is probably not less than 1200 

 feet thick in some places, whilst in others it is reduced to compara- 

 tive insignificance. As a general rule, the breccias and conglo- 

 merates prevail in the lower parts of the series, sandstones, clays, 

 and limestones in the upper ; but everywhere the succession of beds 

 is most irregular and inconstant, thick and important members 

 thinning out and disappearing or totally changing their characters 

 within very short distances. 



None of the Poikilitic rocks of the west of Scotland have as yet 

 yielded fossils capable of determination ; with the exception, indeed, 

 of a few imperfect casts of bivalve shells (Cyrena?) which I found 

 some years ago in a quarry at Ardtornish Towers, I know of no 

 traces of organic remains occurring in the beds. In spite of this 

 absence of fossils, however, their position in the geological series is 

 placed beyond doubt by the following facts : — 



(1) They conformably underlie the Infralias strata of the district. 



(2) They unconformably overlie and overlap the Carboniferous and 

 other Pakeozoic rocks. 



(3) They agree most strikingly in character with strata on the east 

 coast of Scotland, of which the age has been demonstrated by a 

 concurrence of palseontological and stratigraphical evidence. 



Whether particular portions of the strata should be referred to the 

 formations which are elsewhere relegated to the Permian, Trias, and 

 Bhsetic respectively, we are at present wholly unable to determine. 



