It is a reproach, I am aware, sometimes cast upon geological researches, that the portion of the earth’s surface exposed to view is as nothing compared with the entire mass, and that another portion, by far the largest segment, is concealed by the ocean, and its own debris. In addition to these disadvantages, it may now be objected that the line of description indicated narrows the field of research still farther, and that a few disconnected materials only are all that can therefrom be extracted. It may be answered,—“That the earth is constructed with such a degree of uniformity, that a tract of no very large extent may afford instances, in all the leading facts, that we can ever observe in the mineral kingdom. The variety of geological appearances which a traveler meets with, is not at all in proportion to the extent of country he traverses; and if he take in a portion of land sufficient to include primitive and secondary strata, together with mountains, rivers, and plains, and unstratified bodies, in veins and in masses, though it be not a very large part of the earth’s surface, he may find examples of all the most important facts in the history of fossils.”[1] We shall, however, along with our lineal descriptions of the mineral kingdom, notice the occurrence, position, and fossil contents of the strata as represented in other parts of the world.
CHAPTER II.
NATURE AND STRUCTURE OF THE GRAMPIANS. PRIMARY ROCKS.
In beginning a description of the earth, every one is prepared for the information, that it must have existed in some form or other antecedent to the development of life upon its surface. Revelation asserts a succession in the objects created, as well as in all the cosmical arrangements connected with the early history of our planet. Things were not perfected at once, and brought simultaneously into adaptation and form; a preparation and a fitting up, as it were, of the inorganic preceded the introduction of the organic structures of creation; and, accordingly, the solid framework of the globe gives corroborative evidence of this anterior condition of its history. The rocks of the period are, from this circumstance, denominated Primary, because they not merely denote the absence, but are assumed to have been formed before the existence, of any types of organic matter, vegetable or animal.
Nowhere can this first lesson in geology be more forcibly taught than by an examination of the sterile rocks and rapidly decomposing precipices of this bleak and hoary region. Once through the glens, and fairly commencing the ascent of the center mountain, every symptom of existing life has disappeared; and amid the huge, tabular masses that accompany you in the upward journey, there is no trace of organic forms in these vestiges of the past. The nucleus of the whole group is granite, one dense aggregation of crystals; now rent and furrowed by a thousand seams, the heart and penetralia bared and open, a convulsed sea of molten matter still and motionless as the grave! The associated rocks, all of the primary class, are gneiss, mica-slate, quartz-rock, chlorite-slate, and limestone; and these inclose no relic of a living thing. Geology thus ascends the stream of Time; but it gives no farther tidings of a scene like this, save that it arose from the depth beneath at the Creator’s bidding.
The Structure of the District.—The mountain of Ben-Mac-Dhui, according to recent measurements, is 4,418 feet in height, and covers a superficial area of nearly forty miles in extent. It occupies a central position in the Grampian range, being about equidistant betwixt Aberdeen on the German Sea and the western coast, so ribbed and indented by the Atlantic. Ranges of granitoid rocks, of the primary class, diverge for nearly forty miles south and north of Ben-Mac-Dhui, thereby giving this mountain a prominence in position possessed by no other within the boundaries of the island.
The valleys by which this monarch is surrounded, open in every direction, and run toward every point of the compass. Two great rivers, the Don and Dee, take their rise in some of the deep gullies of the mountain, while the Spey is fed by the innumerable streams that issue from its sides. These rivers have each an easterly direction, which, by their water-shed, give shape and character to the whole district. A hundred lateral glens, with their tributary streams, and all their tarn-head or loch, debouch upon the three principal straths, whereby their deepest solitudes are reached, and the very foundations of their loftiest peaks bared and laid open. There, remote from human habitation, the geologist sees as it were two conditions of the world,—the one, the shattered framework and fragments of its early convulsions, huge mountains prostrate and crumbling beneath his feet,—and the other, the spring-heads of renewed vitality collecting in countless dripping rills, each to sustain its own little plot of pasturage and flowerets, not the less welcome that they are all so rare and alpine, and looking in their freshness as if they were there purposely to cicatrize and heal up the deep scars in the rugged precipices around.
Loch-na-gar on the south-east, and Ben-y-gloe on the south-west, have also their separate congeries of lofty hills and precipitous defiles, inclosing tarns, lochs, and rivers; likewise their own peculiar grouping of glens and straths, whose inner recesses are all most speedily attained through the velvet pathways of their moss and crow-berry. From the poetic peak the prospect is worthy of its fame. All around is a vast rolling surface of mountains, with steep mural precipices, and separated by deep ravines, while immediately underneath a cliff of 1,300 feet lies the lake, contracted to a span, and rendered even darker in its gloom by the snowy glaciers that sparkle here and there on the overhanging rocks.
From Loch-na-gar eastward to Craigdarroch and the more distant Morven, and through the great forests of Balloch-bowie, Glentanner, and Glenesk, granite is the prevailing rock. Around Balmoral, immediately under “these steep frowning glories,” the granite rises into a number of smaller and beautifully dome-shaped hills. Cloch-na-bein and Mount Battock, washed by the Feugh and the Dye, are likewise composed of granite. Gneiss, mica-schist, quartz-rock, and clay-slate hang on the southern slopes, training down into the plains of Kincardine and Forfarshire. To the west of Loch-na-gar, and intermediate betwixt that range and the granitoid masses which cluster round Ben-Mac-Dhui, the same alternating series of stratified rocks occur. From Castleton to the head of Loch Callater, and along by Glen-clunie to the junction with Glen-beg, where the counties of Aberdeen and Perth meet, the strike of these rocks is again passed over in a walk of a few miles; the beds penetrated and tilted up by veins of granite and feldspar. Several dykes of the latter mineral, of an extremely deep-red color and glassy crystalline texture, traverse the district, extending over a vast range of country, penetrating indifferently the granites and schists, and always forming attractive objects in the beds of the rivers.
In the immediate vicinity of Castleton and Invercauld, the geological phenomena of the district are very accessible as well as instructive, in consequence of the comparative smallness of the mountains, and isolated position into which they are thrown. A magnificent amphitheater of hill and plain is spread out before the traveler, through which the Dee, after a course of upward of twenty miles from its wells—mysterious as the fountains of the Nile—rolls its waters, now joined by the Quioch, Clunie, Candlie, and all the tributaries of the surrounding peaks. Some of the hills present bare precipitous cliffs, as Craig Koynach and the Lion’s Face, where the granite, schistose, and calcareous rocks are finely exposed to view. Their strike is continued westward, when they are severally crossed in the easy ascent of Morne, half of whose dome-shaped top is covered with quartz-rock, which here, as in most of the neighboring heights, attains to an enormous thickness, and shows in weathering the yellow granular texture of sandstone. So remarkably like are some specimens we picked up by the roadside, that for a time we imagined ourselves to be approaching a region of secondary deposits. Internally, however, the bright crystalline structure is uninvaded by decay. Ben-Beck, Cairn-a-drochel, and Ben-Viach behind Mar Lodge, are chiefly composed of gneiss, passing into a slaty micaceous schist. The same character of rock continues upward through Glen-lui until its junction with Glen-lui-beg and Glen-derry, where the granite maintains its sovereignty over all that primitive lofty region.