Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/156

 east coast of Scotland, consist almost exclusively of more or less isolated patches, often of small extent, on the shores of the Moray Firth. It is possible that the Boulder-clays and other drifts, which attain to so great a thickness in the north-east of Scotland, may conceal other similar patches ; these we can only expect to be revealed to our observation through some favourable combination of circumstances, in deep natural or artificial sections.

The masses of Mesozoic strata which are seen at various points round the Moray Firth, are found lying indiscriminately against the different Palaeozoic rocks — namely, the several members of the Old Red Sandstone, the metamorphic rocks of the Lower Silurian, and the great bosses of granite. The Secondary strata are usually greatly bent and faulted, and often, especially near their junction with the Palaeozoic rocks, very violently contorted. The strata are shown by their palaeontological characters to be of various ages, from the Trias to the Upper Oolite, and, as will appear from the present memoir, enable us to reconstruct nearly the whole of the Jurassic series as developed in this northern district.

None of the beds exhibit evidence of having been beaches lying upon the old Palaeozoic rocks with which they are now in contact, and made up of their fragments. Common as this phenomenon is, as we shall see hereafter, on the west coast of Scotland, we find nothing resembling it on the east coast, where the conglomerates and grits are never made up of the detritus of the primary rocks lying nearest to them ; but on the contrary the various beds of the series exhibit indications of the most various modes of origin — deep-sea marine, shallow-water marine, littoral, brackish-water, freshwater, and terrestrial.

It is evident on an examination of these patches of Secondary strata that they form the last remaining vestiges of extensive formations which once covered considerable areas, but have been almost wholly removed by the enormous denudation to which the district in which they are developed has been subjected; it is equally plain that the present position of the patches among the older rocks must be ascribed to accidental causes, which have operated since their original deposition. In almost every instance we can trace the proximate causes of the preservation of the patches, either in the presence of rocks of especial hardness and capability of resisting denuding influences, like the cherty rock of Stotfield, the indurated sandstones of Braamberry Hill, the hard grits of Kintradwell and the breccias of Helmsdale — or in the position and protective influence of surrounding masses of Palaeozoic rocks, as at Eathie and Shandwick. The more remote causes which have contributed to the preservation of the several patches I shall presently demonstrate. That, even as late as the glacial period, the Secondary rocks covered much more extensive areas than at present appears to be proved by the great abundance of their fragments in the Boulder-clay of the east of Scotland.

The areas covered by the Secondary rocks which have been as yet discovered are, as already intimated, very small ; and as they are