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Page:Popular Science Monthly Volume 65.djvu/387

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383
THE PROGRESS OF SCIENCE.

Mr. E. J. Garwood thus describes the Whin Sill, Hugh Force, Teesdale: This is a classical waterfall, described by Sedgwick in 1823, Wm. Button in 1831 and Phillips in 1836. The fall is 70 feet high, over the Whin Sill, which is here intrusive in the Lower Yoredale Beds. The photograph shows the chief fall near the right bank of the Tees. It is working along a joint in the hard Whin which forms the protective cap to the fall; when in flood surplus water also pours through a second joint near the left bank. The undercutting of the limestone is shown by the caves and the hanging icicles; the gorge below bears testimony to the recession of the falls. The section is as follows: Whin sill, 30 feet; shale, thinning out, 2 feet; whin, 9 feet; shale, altered, with superinduced prismatic jointing, 15 feet; hard limestone, with pyrites, 8 feet; hard, fossiliferous, crinoidal limestone, 20 feet; coralline limestone, 6 feet. The limestone is altered and saccharoidal to a distance of 35 feet below the base of the whin; the latter is of the normal type described by Teall.

PSM V65 D387 Natural arch at torquay.png

Natural Arch at Torquay.

Mr. W. A. E. Ussher gives an account of the natural arch at Torquay: The natural arch depicted in the photograph forms a conspicuous object on the south coast of the Torquay Promontory between the Bath Saloons and Daddy Hole. It has been tunneled by the sea through a small headland near the axis of an inverted synclinal curve in Middle Devonian Limestones. The prolongation of this axis eastward is well shown on the coast a quarter of a mile away. In the middle and lower part of the limestone masses of Torquay, a partial cleavage is often displayed by the beds, consequent on the pressure which has produced the folding in them; this structure, as shown in the photograph, becomes in certain cases most pronounced at and near the axis of the folds, causing a shattering of the rock at the point where the direction of strain cleavage approximates to, or coincides with, the inverted bedding I planes. The dark marking extending