J. W. JTTDD ON THE SECONDARY ROCKS OE SCOTLAND. 689 



In addition to these general remarks on the stratigraphical rela- 

 tions of the Poikilitic strata of the Western Highlands, it is only 

 necessary to add that at Grain ard Bay, in Eaasay, and in Sleat these 

 strata rest on the Torridon Sandstones ; in Strath, Ardnamurchan, 

 Inch Kenneth, Gribun, and ronnd Loch Arienas on the old gneissic 

 rocks of the county : and at the Innimore of Ardtornish upon Carbo- 

 niferous deposits. AtGruinard Bay they are not seen to be covered 

 by any younger formation except the glacial deposit ; but at Eaasay, 

 Sleat, and Ardnamurchan they are followed by highly fossiliferous 

 Infralias strata, apparently everywhere in perfectly conformable 

 succession ; while at Sleat, Inch Kenneth, Gribun, Loch Aline, and 

 in the remarkable outliers of Morvem they are unconformably over- 

 lain, sometimes by the Upper Cretaceous strata, and at others by the 

 great masses of Tertiary lava. 



After this general account of the formation in question, it will 

 only be necessary to add some remarks on the peculiarities presented 

 by the different sections of its beds, which occur over an area 

 stretching nearly 120 miles in length, from Gruinard Bay in the 

 north to Gribun in the south. 



At Gruinard Bay the Poikilitic strata are well exhibited in a 

 succession of sea-cliff and and shore-reef sections, stretching for a 

 distance of over three miles. Inland they are wholly covered and 

 concealed by boulder-clay and peat-mosses. As already pointed out, 

 they owe their position and preservation to the action of grand faults 

 of certainly vast but indeterminate amount of throw, by which they 

 are brought far beloAV their original position and troughed into the 

 heart of the Torridon-sandstone masses. Several parallel faults 

 traverse this down-dropped relic of strata; and its beds show many 

 signs of the subterranean disturbances to which they have been sub- 

 jected* (see the section, fig. 1, p. 671). 



The unconformable relations of these Poikilitic deposits to the 

 Torridon sandstones, on which they rest, has been dwelt upon and 

 well illustrated by both Maccullochf and NicolJ, who have accom- 

 plished so much in unearthing the secrets of Highland geology. 

 These unconformable relations are of the most striking and unmis- 

 takable character — the Poikilitic beds dipping generally W. or N.W., 

 while the underlying Torridon sandstones lie at very high angles, 

 with varying strike, and are sometimes vertical and at others contorted. 

 The little sketch of a boat-house given by Prof. Nicol, the walls of 

 which are formed of Torridon sandstone, and the roof of Poikilitic 

 strata, serves to give some idea of the very striking appearances that 

 may be witnessed along this interesting shore. The section I have 

 already given shows how the Poikilitic strata are bent into gentle 

 folds, and are faulted and interrupted along the shores of Gruinard Bay. 



In company with my friend Dr. Taylor Smith I estimated the 

 thickness and succession of the Poikilitic beds as exposed in a con- 

 tinuous series of sections between the salmon-house west of Sands, 



* ' Western Isles of Scotland', Atlasplate xxxii. fig. 8. 

 t Quart. Journ. Geol. Soe. vol. xiv. p. 168. 

 t Ibid. vol. xiv. (1858), p. 168. 



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