The course of creation

by John Anderson

CHAPTER V.
YELLOW SANDSTONE.

Dura Den, whither the scene of our explorations now shifts, occupies a central position in Fifeshire, and lies equidistant betwixt St. Andrews and Cupar, the county town. This classic field of geology is therefore of the easiest access. The railway traverses the opening to the ravine, a lovely valley of choice archæological as well as fossil remains, where parliaments have assembled and a scepter was contended for, the retreat of learned churchmen, and a refuge in the caverns of its rock for persecuted saints. A day’s excursion to such a place cannot fail to be a profitable as well as agreeable one, where the students of geology, or of botany, or of history, will severally meet with objects suitable to their taste; and, if lovers of the tragic, a short detour to the left will furnish a sight of Magus Muir, of cruel memory and most indefensible policy.

The geological structure of Dura Den is more than ordinarily interesting, presenting, as it does within a limited distance, and in close juxtaposition, the two series of the old red sandstone and carboniferous systems, an included mass of overlying trap, a greenstone dyke, and a vein of galena. The whole length of the dell, with its windings, from the ruins of the castle resting on the conglomerate red, to the outgoing on the south into Ceres basin of the coal formation, does not exceed a mile and a half. The rocks overhang the road which passes through the valley, the sandstone in some places rising precipitously into bold mural cliffs of a hundred feet in height, and presenting colored and well-defined sections of the different layers of which it is composed. These constitute the fish beds of the yellow sandstone group, lying toward the northern extremity of the den, and consist of beds of variegated marls, intermixed with friable arenaceous bands, and hard, compact, fine-grained building stone.

The carboniferous series are separated from those of the yellow sandstone by the greenstone dyke referred to, which immediately, and inconveniently for sight of the junction, interposes betwixt the two systems. The lower beds of the independent coal formation are here thrown up to an angle of 26°, the yellow sandstone adjacent being nearly horizontal, and in no place exceeding an inclination of eight or ten degrees. The coal beds have been lifted up by and repose anticlinally upon the trap, where the cutting for the road has exposed the outcrop of the seams; and thus, in a narrow space and lying on the surface, we may mark the outgoing and the incoming of a vast revolutionary epoch, organic and inorganic, in the earth’s history. The strata, consisting of alternating bands of coal, shale, ironstone, and sandstone, assume toward the head of the valley a nearly horizontal position, abutting against a mass of trap which separates the lower from the upper workable beds of the bituminous mineral in the Ceres basin.

Dura Den, in addition to the interest arising from lithological structure, presents an excellent example of a valley of erosion. The river which traverses it rises at times into considerable volume, and sweeps with violence through the pass; connected above, at one period, with a lake, and acting continuously on soft friable matter, the abrading powers of the instrument are sufficiently adequate to the production of the effect. The qualities of the rocks penetrated may be easily inferred from the windings of the stream—the harder substances occasioning a divergence from the straight course—the soft and marly scooped out into wider and more extended areas. A section of any one of them is thereby labeled for the fullest inspection, which are arranged, not perpendicularly one upon another, but drawn out in longitudinal succession on the floor and sidewalls of the valley, and exhibiting to the geologist, after so many types and forms of the old red sandstone, the first break and most northern limit of the coal metals in the great central basin of Scotland.

The Yellow Sandstone, as it is termed from its prevailing color, though not uniformly so, belongs to the old red or devonian system of rocks, of which the cornstone and conglomerate beds are in the immediate vicinity, and the position and relation of the three to one another easily determinable. The upper or yellow deposit occupies the valley of Stratheden nearly throughout its entire length and breadth, and ranges along the base of the heights of Nydie, Cults, the Lomonds, Binnarty, and the Cleish hills, dipping under the carboniferous lower group, and generally separated by overlying masses of trap. The sandstones, indeed, of both systems, resemble each other so much in color and texture, that in many instances along the line now indicated the trap must be taken as a guide by which to ascertain the qualities and respective positions of the two series. Glenvale, a beautiful ravine which intersects the Lomond range, presents admirable sections of the whole group, in their regular order of superposition and finely displaying their contrasting mineral characters.

Organic Remains. These are abundantly distributed in scales, teeth, spines, coprolites, and other remains, and are to be found in every opening and quarry throughout the range of the deposit. It is only in Dura Den, however, that any entire animal forms have as yet been obtained, and these all confined to a portion of the rock not exceeding thirty yards by three in breadth, a narrow trough excavated for the purpose of forming a water-shed to the mill, which stands in the center of the valley. The fossils derived from this single spot consist of four new genera, and seven or eight new species, that have been added to our catalogue of extinct animals. These remains were all in a state of beautiful preservation; the scales and fins are brightly enameled, and contrasted with the matrix in which they are set, the colors are as vivid and glistening as when the animals were sporting in their native element. The specimens, I believe, of the various collections made in this rich depository by different parties were all submitted to the examination of M. Agassiz, who has figured several of them in his “Monograph” on the old red sandstone, but without completing, it is much to be regretted, his descriptions of the various fossils. We give the following abridgment of such descriptions as are contained in the work.

There are two new species of Holoptychius represented, namely, Andersoni and Flemingii, and these are distinguished entirely by the form and tracery of their respective scales. The H. Andersoni is described as a small spindle-shaped (fusiforme) fish, thick and short, and narrowing rapidly toward the tail.