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Updated: May 21, 2025
They are made up in great part of finely laminated silt, alternating with coarser materials, through which stones from 4 to 5 feet in length are scattered. These large boulders, and some smaller ones, are polished on one or more sides, and marked with glacial striae.
The proofs of such a glacier having actually existed at the point in question consist, he says, in numerous cross striae observable in the bottom of Glen Spean, and in the presence of moraine matter in considerable abundance on the flanks of the hill extending to heights above the Glen Glaster col.
They are common even in cases where there has been no shift, and occur equally in non-metalliferous fissures. They are called by miners "slicken- sides," from the German schlichten, to plane, and seite, side. It is supposed that the lines of the striae indicate the direction in which the rocks were moved.
Fortunately, the deep striae or furrows in the surface of the rocks that made the bottom of the ravine in some degree facilitated their progress, but it was not until they had been toiling up for two hours more that they succeeded in reaching the summit of the cliff. Eagerly and anxiously did they look around.
They exhibit in the telescope a gradation from somewhat coarse grooves, easily visible at suitable times in very moderately sized instruments, to striae so delicate as to require the largest and most perfect optical means and the best atmospheric conditions to be glimpsed at all.
Magnificent crystals have been found in these localities in times long past, and from the fragments and sections of crystals found in the débris of early explorations we observed the wide range of color and the deep longitudinal striae which characterize the renowned beryls from the Altai Mountains, in Siberia.
In the same countries, erratic blocks have travelled from north to south, following the same direction as the glacial furrows and striae imprinted almost everywhere on the solid rocks underlying the drift.
They have been traced in the Alps to great heights above the present glaciers, and to great horizontal distances beyond them. The moraines, erratics, polished surfaces, domes, and striae, above described, are observed in the great valley of Switzerland, fifty miles broad; and almost everywhere on the Jura, a chain which lies to the north of this valley.
The face of each wall of the fissure is often beautifully polished, as if glazed, striated, or scored with parallel furrows and ridges, such as would be produced by the continued rubbing together of surfaces of unequal hardness. These polished surfaces are called by miners "slickensides." It is supposed that the lines of the striae indicate the direction in which the rocks were moved.
I have thus far directed attention only to the most recent and appreciable of the phenomena; but it must be borne in mind that less recent and less obvious traces of glacial action abound on ALL the ranges throughout the entire basin, where the fine striae and grooves have been obliterated, and most of the moraines have been washed away, or so modified as to be no longer recognizable, and even the lakes and meadows, so characteristic of glacial regions, have almost entirely vanished.
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