68 Notices of Memoirs — 



the Coal-measnres. There is some reason to believe that in this area 

 one or more lakes existed in preglacial times. 



The boulders in the drifts at Colomendey are chiefly limestone, 

 though felstone is likewise present. Many of the smaller stones 

 consist of vein quai'tz and Wenlock shale or grit. The fact that 

 many of the stones must have come from some . distance, and a few 

 of them (the felstones) from a great distance, is sufficient to show 

 that the drifts could not have been deposited by a cause limited to 

 this particular hollow, and that here they must either have been 

 arrested, while in exposed situations no deposition took place, or 

 that a more extensive deposition was followed by denudation, which 

 left this patch on account of its being protected. The preglacial 

 white clay is probably a freshwater deposit. The overlying drifts 

 must have been accumulated by the sea, floating ice, land ice, or by 

 these three agencies combined. It is worthy of remark that many of 

 the small stones in the blue clay are much rounded, as if they had been 

 subjected to attrition under water. This clay evidently belongs to 

 the oldest drift yet discovered in the north-west of England and 

 Wales. On washing it, its structure is found to differ from that of 

 the lower brown clay of the plains, and likewise from that of the 

 pinnel of the Lake District. With a hummocky and much denuded 

 surface, a similar blue clay is found underlying these deposits on the 

 coast of North Wales and in Cumberland.^ 



nsroTioiES OIF n^fiiEiynoiE/S. 



I. — The Second aky Eocks op Scotland. (Second Paper.) On 

 THE Ancient Volcanos of the Highlands, and their Eela- 



TIONS TO THE MeSOZOIO StEATA.^ 



By John W. Jtjdd, F.G.S. 



Introduction. — The vestiges of the Secondary strata on the west 

 coast of Scotland have been preserved, like the interesting relics 

 of Pompeii, by being buried under the products of volcanic erup- 

 tions. The deposition of the Mesozoic strata in this district was 

 both preceded and followed by exhibitions of volcanic phenomena 

 on the grandest scale ; and it is only by a careful study of the 

 records of these two great periods of igneous activity that we can 

 hope to understand the remarkable relations of the fragments of the 

 intermediate sedimentary formations, or to account for the peculiari- 

 ties which they present. 



That the rocks forming the great plateaux of the Hebrides and 

 the north of Ireland are really the vestiges of innumerable lava- 

 streams, is a fact which has long been recognized by geologists. 

 That these lavas were of suhaerial and not subaqueous origin, is 

 proved by the absence of all contemporaneous interbedded sedi- 

 mentary rocks, by the evidently terrestrial origin of the surfaces on 

 which they lie, and by the intercalation among them of old soils, 



1 See Geol. Mag. Vol. VII. Oct. and Dec. 1870, and Vol. IX. January, 1872. 

 ^ Abstract of a paper communicated to the Geological Society on January 21, 1874, 



