A cliff of shale seldom shows much of the picturesque, though often a good deal of the ruinous. The rock is easily undermined by streams, and a shale ravine usually exhibits in consequence either heaps of crumbling rubbish, or, where the stream comes past with a more rapid current, perpendicular walls, jointed and laminated, but without much variety of outline. Such cliffs, however, merit the careful attention of the observer, for from their friability they are most easily decomposed and washed down by streams, to form new accumulations of similar soft argillaceous matter. A shale coast-line sometimes shows cliffs of considerable altitude, as in some parts of Skye and Pabba, where the Lias shales may be seen piled over each other often to a height of seventy or eighty feet, and spreading out along the shore as low flat reefs and skerries, brown with algæ at their seaward ends, and showing on the higher slopes of the beach the characteristic fossils of the Lias--_ammonites_, _belemnites_, and _gryphææ_--crowded together by hundreds. The action of the decomposing forces has operated more effectually on the soft material of the shale than on the hard crystalline lime of the included shells, so that the latter stand out in relief from the dull-brown surface of the rock, and from their numbers and prominence form one of the most marked features of the coast-line. Probably few have ever visited a limestone district without marking the manner in which that rock yields to the action of the elements, whether in an inland part of the country where rivers have cut deep gullies through the rock, or along some exposed shore where the stone has been wasted by a still ruder assailant. An exposed cliff of hard homogeneous limestone weathers into deep clefts and holes; the entire surface assumes a pitted appearance, somewhat like a sandy beach after a showier of rain, and the planes of stratification, or lines formed by the parallel junction of the beds are often worn away until the rock looks not unlike a piece of old masonry, in which the mortar has decayed and dropped out, leaving the angles of the stones to get wasted and rounded by the action of the weather. In many districts, too, where the rock is richly fossiliferous, the broken joints of encrinites along with corals and shells may be seen crowded together by myriads, their hard skeletons protruding from the wasted rock in such a way as to show that the stone can contain very little else. By this means we often learn that a limestone bed is nothing but an old sea-bottom, where the calcareous sediment was mainly derived from broken stone-lilies, corals, and shells, though if we break off a piece of the rock the internal fracture may show very little or no trace of any organic structure. And hence if the geologist would form an accurate conception of the origin and structure of many of the stratified rocks, he must study them not in hand specimens neatly trimmed and arranged along the