SCENERY-ITS

CHARACTERISTICS

AND CAUSES.

As the surface-configuration of the earth is infinitely varied, so the causes of that diversity, whether internal or external, must vary in a corresponding degree. Variety of aspect and contrast involve, in fact, dissimilarity of producing agency--complexity in the one being but the natural result of diversity in the other. Here we have plains that are spoken of as tame and monotonous, there fens and moors described as waste and dreary; here hills and dales regarded as gentle and pleasing, there crags and glens as picturesque and romantic; here splintery cliffs and precipitous gorges viewed as wild and awful, and there mountain-peaks and shaggy ravines invested with the attributes of grandeur and sublimity. This surface-diversity or scenery, so long the theme of the poet and painter, is not less the subject of the geographer and geologist. The former take it as they find it, and describe it in words, or transfer it to their canvas; the latter, equally appreciating its variety, attempt to arrive at its intimate nature and producing causes. In this, as in other efforts to interpret phenomena, diversity of opinion is naturally expected; and hence, at the present time, scenery is one of the moot points of Geology-some attributing it mainly to external agencies

of waste and reconstruction, some to internal agencies of upheaval and depression, and others, taking a broader and more catholic view, partly to internal and partly to external causes. Let us try, within the compass of a few pages, to explain that all scenery or surface-diversity is owing partly to the agents of waste and reconstruction that are ever transferring and remodelling the crust of the earth; partly to geological structure, or the nature of the rocks on which these forces operate; partly to geographical position, or the conditions under which they act; and partly to the time that any portion of the terrestrial surface has been subjected to their operations.

In the first place, it requires little effort to perceive that whatever the original surface-configuration of any part of the earth's crust-island or continent-that configuration must be incessantly undergoing change and modification. Attacked from without by frosts, rains, and rivers, by waves, tides, and currents, its rocky asperities will be gradually worn and rounded, its depressions more deeply excavated, and its shores rendered more rugged and irregular. Frosts must split and crumble, glacier grind and smooth, rains soften and wash away, rivers erode, waves degrade, and tidal currents scour and transport. And just as these forces from without are incessantly remodelling the surface-configuration, so the forces from within-the volcano, earthquake, and crust-movement—are as ceaselessly operating towards the same end: the volcano by the accumulation of new hills; the earthquake by the production of elevations, depressions, and fractures; and the crust-movement by slow and gradual uprise of some regions, and by equally slow and gradual submergence of others. Depending on the earth's primal and cosmical relations, these agencies are ceaseless and enduring; and to them, therefore, and the nature of the rocks on which they operate, the geographical

conditions under which they appear, and the time they have acted, must the surface-diversity of the earth be largely ascribed. Of course, as each agent has its own peculiar mode of action, the results will generally give evidence of the producing cause; but in many instances where several agencies have acted simultaneously, or where one agent has been succeeded by another, the results will be greatly complicated, and it becomes impossible to do more than indicate in a very general way the forces that have been instrumental in their production.

In the second place, it must be equally evident, even to the most casual inquirer, that geological structure is one of the fundamental causes of surface-diversity. The alluvial plain, from the soft and recent nature of its deposits, must always be more or less flat and uniform in surface. Linklands and sandy deserts, from the shifting character of their material, must be abruptly uneven and irregular, and though on the large scale as monotonous as the alluvial plain, yet within limited areas may present not unpleasing diversity. Chalk hills, from the soft and homogeneous texture of their rocks, weather into rounded and easy undulations; hence the softened outlines of the downs and coombs of southern England. Limestone strata, being of a harder texture, but of fissured and jointed structure, break up into wall-like scaurs and precipices and tabletopped heights; hence a main cause for the peculiar scenery of the Dolomite mountains, and for many of the features in the dales of Derbyshire and western Yorkshire. Volcanic hills, being chiefly products of eruption, assume a conical form-regularly conical or "sugar-loaf," like the Peak of Teneriffe-when made up of loose cindery material; irregularly conical, like Etna, when consisting partly of scoriæ and partly of lava; and more flatly conical, like Hecla, when mainly composed of lava, which, from its molten

nature, must always rest at a lower angle. Trap hills, on the other hand, built up of old volcanic ejections, now converted into tuffs and greenstones and basalts, present (like those of the Scottish Lowlands) more or less a terraced outline-the softer tufa having weathered into slopes, and the interbedded basalts and greenstones standing out as steps and terraces. Granites and porphyries weather slowly into bald, round-shouldered mountains, like the Grampians— sterile, heath-clad, and dreary, because of the hard, uniform, and resisting character of the rocks. Slaty and schistose formations, usually standing at high angles, and consisting of harder and softer strata, present jagged peaks and pinnacles, the weirdest of heights and the wildest of gorges.

The stream that erodes for itself a valley through a soft formation, can only cut for its waters a narrow ravine through harder strata. The river that flows smoothly in its channel through beds of uniform consistency, becomes a noisy cataract through rocks of unequal resistance, or plunges in noisy tumult over some harder ledge or intersecting dyke into the softer strata below. Over widespread formations, consisting of strata of unequal hardness, the courses of the streams are generally determined by the strike of the softer beds; and thus arise those undulations of hill and vale-the former representing the sandstones and limestones, and the latter the clays and shales. The sea-cliff of uniform formation may stand like an even wall for ages; that of irregular resistance will be gouged into gorge and gully of the wildest description. And for the same reason this promontory may stand bald and bare and unbroken through all time, while that may be hewn into arch and stack and needle by the restless surge of the waters. In fine, no geologist can glance at the diversity of the terrestrial surface without being instantly convinced that the varying nature of rocks and rock-formations is one

of the fundamental causes of that diversity and configuration. And just as the rock-structure is uniform or varied, just as it lies unbroken or disturbed by volcanic agency from below, so will the surfaces it presents be uniform or irregular, abruptly thrown into heights or sunk into hollows. In geological structure, therefore, we find a main cause of surface-configuration; and he who best understands the geology of a country will be best qualified to appreciate the diversity of its scenery.

In the third place, it must also be obvious that whatever the geological structure, that structure will be variously affected according to the geographical position of the country in which it occurs. What will take place under the glacial influence of the polar regions cannot occur under the temperate zones; and what may happen under the alternate frosts and thaws of temperate latitudes will not be produced under the uniform climate of the tropics. Rocks that may be weathered and worn into the tamest outlines in a variable climate like Britain, may stand out bold and precipitous for ages in one like that of Egypt. The cliffs and precipices that may rise unbroken for centuries in lower latitudes would be split and fractured into a thousand fragments by the frosts of boreal latitudes and glacial heights. The same rocks that are gouged and furrowed by the rains and runnels on the eastern slopes of the Andes, remain intact on the rainless counter-slopes of Peru. The volcanic mountains of the East Indian Archipelago, that are seamed and channeled by the monsoon-rains to the height of eight or ten thousand feet, rear their cindery cones smooth and unbroken beyond that elevation. Far above the snow-line the clefts and precipices of moistureless mountains, like the central Andes, may remain rugged and untouched, as formed by the volcano or fractured by the earthquake; while in moister regions at the same altitudes