Conclusion. Although, as I have before stated, it has been thought advisable to postpone the discussion of the numerous problems of interest which suggest themselves to the student of the remarkable relics of the Secondary rocks in the Scottish Highlands, until the fourth and concluding portion of this memoir is published—yet there are several questions which at the present time engage the minds of geologists upon which, as it appears to me, the facts and arguments of the present part of this memoir have an important bearing; and these it may not be undesirable to notice briefly at the present stage of the inquiry. Other and more general discussions will be allowed to stand over till such time as I have made the proposed comparison between the characters and modes of preservation of the beds under consideration and those of their equivalents in Ireland, England, Scandinavia, and other portions of the Continent. I may briefly point out in the first place the great interest which attaches to the fact that there exists in the north-western part of the British archipelago a series of strata of Cretaceous age exhibiting evidence of the prevalence of estuarine alternating with marine conditions. The great and deserved amount of attention which is now directed to the similar beds, developed on such a grand scale in Western America, renders the discovery of the minute Scottish representatives of the period particularly important at the present time. It is tantalizing, however, to the British geologist to have to