Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/144

 indefatigable observers at many points, we are now able to perceive that the districts at present constituting England, Northern France, and Western Germany were included during the Jurassic and Neocomian periods within a single marine province, the very uniform succession of life in which has been clearly traced. Thus a palaeontological scale has been constructed which, with due precautions, may be safely used for the determination of the age of any isolated rock-masses which were deposited within the limits of this old marine province. Further, the relations of the different strata and the conditions under which they were deposited at various points have been so far investigated that some progress has been made in determining the boundaries of the several gulfs, channels, and islands of that great sea and archipelago which constituted this life-province. This, in turn, has led to the recognition and study of the minor palaeontological features which characterized the several subdivisions of that sea, and, in a much less degree (owing to the paucity of the evidence), of the several land-areas which bounded them.

Lastly, a considerable amount of knowledge has been gained of the succession of the movements of upheaval and subsidence by which the boundaries of the sea and land within this area were at different periods modified.

To the interesting patches of Jurassic strata in the Highlands of Scotland, then, we resort, and, in spite of the fragmentary character of the evidence in many instances, seek in them for the solution of many problems of the highest geological interest, among which we may especially instance the following : —

(1) The determination of the northern limits of the old life-province to which we have referred, and the question whether the Scotch deposits were formed within it.

(2) The special palaeontological features of the province or subdivision of a province to which these strata belong.

(3) The conditions under which the various beds constituting the Mesozoic series in Scotland were deposited.

(4) The influence of climate in affecting the modes of deposition, and consequent character, of the rocks, and also in modifying the palaeontological features of the area.

(5) The position and extent, with the nature and productions, of the lands bounding this portion of the old Mesozoic sea.

(6) The character and succession of the subterranean movements which affected the area during the Jurassic and subsequent epochs.

On each of these problems the study of the Highland strata throws important light ; and to some of them it affords satisfactory and complete solutions. That in a case like the present, where the rocks preserved and exposed are of such a fragmentary character, some unfortunate gaps in the evidence will have to be lamented, is of course no more than might be anticipated ; yet I hope to be able to show in the sequel that, by a careful examination, with the aid of the palaeontological key, of every trace of these rocks left to us, the cases of total hiatus in the evidence are reduced to a remarkably small number, and that we are, in fact, able to sketch with