Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/461

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Dr. Mac Culloch on Quartz Rock.

in breadth from one mile to six, is fundamentally composed of this one rock, which is also to be found extending through Scarba on its northern, and through a great portion of Isla on its southern shore. The other rocks which occur, with the exception of an important series to be immediately described, either occupy small spaces apparently subordinate to the general mass, or consist of veins which traverse it. The highest part of this tract forms an irregular elevation, of which the three well known Paps of Jura attaining the height of 2500 or 2600 feet, are the most remarkable and prominent features. These occupy a point in the island much nearer to the southern than to the northern extremity, The interval between them and the southern shore is low, the mountains declining with a tolerably uninterrupted slope to the sea. But that between the Paps and the northern side is occupied by a succession of hills which also decline gradually from the highest elevation, and form a broken ridge extending to the northern shore of the island. If we look from any of the highest summits towards the north, a view of almost unexampled singularity and grandeur is afforded. A series of ridges and broken elevations appears under the eye, but so far beneath it that their irregularities are nearly lost in the continuity of the straight lines which guide the sight to the further extremity of their range. These seem to rise from beneath the feet, and to converge to as distant centre, according to the strict laws of perspective. On investigating the cause of this striking disposition, it is easy to perceive that the effect is produced by the disrupted edges of strata of rock rising from the east at a considerable angle, and broken away towards the west.

However much the continuity be here and there apparently interrupted by the predominance of some particular hill, it is obvious

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