Topiary

“ The structure of the former belongs properly with the original structures of the volcanic rocks; but the latter—the true mountains—owe their internal structure and altitude or relief almost wholly to the crumpling and mashing together of great zones of the earth’s crust, being, as already pointed out, the culminating points of the plication, cleavage, and faulting of the strata. “A mountain-chain consists of a great plateau or bulge of the earth’s surface, often hundreds of miles wide and thousands of miles long. ”

“ The patient study of the rocks has revealed the origin of the present configuration of the land. There is not a hill or valley, not a plateau or mountain-region, which does not reveal its own history. The geologist can tell you why continents are bordered by coast-ranges, and why their interiors are generally comparatively low and basin-shaped. The oceanic basins and continental areas, we learn, are primeval wrinkles in the earth’s crust, caused by its irregular subsidence upon the gradually cooling and contracting nucleus. ”

“ The Hills and Valleys.—Sir Charles Warren was the first to point out the necessity of ascertaining the depth of the rock below the present surface, in as many places as possible, and of referring all the measurements to one fixed datum, the level of the sea. In the study of the ancient topography the original appearance of the ground is the first consideration, for although a certain amount of soil may always have existed, still the ancient surface must have conformed far more closely to that of the rock than does the present. ”

“ This character of the coast is particularly favourable to the pursuits of the geologist, laying open to him, in every direction, by the most splendid natural sections, the structure and relations of the rocks of which the country is composed. Nor is the physiognomy of the rocks in the interior less remarkable. On every hill the granite is seen protruding in the most fantastic forms from the scanty and imperfect covering of soil. ”

“ The tors—Nature's towers—are huge masses of granite on the top of the hills, which are not high enough to be called mountains, piled one upon another in Nature's own fantastic way. There may be a tor, or a group of tors, crowning an eminence, but the effect, either near or afar, is to give the hilltop a grand and imposing look. ”

“ Simply this, that a lake or reservoir on the top of a mountain means the existence of a spring or springs. Now springs in granite or hard slate do not wear away the substance of the rock in the same way as they do when they come through limestone. And moreover, the natures of the two rocks are quite different. There are fissures and cavities in the limestone which are wanting, or which are at any rate not so common or perpetually recurrent in the other rock. ”

“ The bed of the ocean, like the face of the land, is affected by elevations and depressions, and its deepest points are about as far below its surface as the highest mountains are above it. There are areas of the sea bottom which, as a whole, may be compared to the plains of the land, and others which may be likened to plateaus, and the lines of gradation between them are as indistinct as they often are on the land. There are mountain peaks, chiefly of volcanic origin, and depressions comparable to the great basins on the land. ”

“ But most of the mountain ranges of the earth, and some of the greatest, such as the Alps and the Himalayas, were originally mountains of folding. The earth's crust has wrinkled into a fold; or into a series of folds, forming a series of parallel ridges and intervening valleys; or a number of folds have been mashed together into a vast upswelling of the crust, in which the layers have been so crumpled and twisted, overturned and crushed, that it is exceedingly difficult to make out the original structure. ”

“ Here the science of geology takes its start with the metamorphic rocks, and it is the dividing line between the inner, smaller, and the outer, larger, planets.
IV. The Terraqueous Stage, when the surface has become substantially stable, there are great oceans gradually diminishing in size, and land gradually increasing. This is the stage of the sedimentary rocks, the time when the planet passes from its own supply of heat to dependence upon that of the sun; the stage when life begins, and the one in which the Earth is now. ”

“ Petrology is the complement of lithology, and in many respects it is the most fascinating division of geology, since in no other direction in this science are we brought constantly into such intimate relations with the beautiful and sublime in nature. The structures of rocks are the basis of nearly all natural scenery; for what we call scenery is usually merely the external expression, as developed by the powerful but delicate sculpture of the agents of erosion—rain and frost, rivers and glaciers, etc.—of the geological structure of the country. ”

“ The inclinations of the surface of the solid crust of the earth vary much, according to the different qualities of the rocks; some having a tendency to form abrupt precipices, others, again, to produce gentle declivities. [463] For this reason, mountains consisting of quartz or porphyry, for example, very frequently present surfaces destitute of vegetation; while, on the other hand, those of granite, slate or sandstone, are more frequently adapted for agriculture and planting. ”

“ The contrast between the smoothly-flowing contour of the lower elevations and the shattered and riven aspect of the harsh ridges, sharp peaks, and craggy tors above, is particularly striking. The mammillated and dome-shaped masses have a pale, ghastly grey hue, their broad bare surfaces reflecting the light freely, while at higher elevations the abundant irregularities of the rocks throw many shadows, and impart a darker aspect to the mountain-tops. ”

“ To all these Professor Forbes assigns the characteristic regions of depth, nature of favourite ground, and geographical distribution. The most positive and determining influence is that of the ground or sea-bottom. "According as rock, sand, mud, weedy or gravelly ground prevails, so will the numbers of the several genera and species vary. The presence of the sponges of commerce often depends on the rising up of peaks of rock in the deep water near the coast. ”

“ I also had a clear view of the coast mountains for a hundred miles or thereabouts, all of which are tellingly glaciated in harmony with the above generalization. Most of the rock is granite with cleavage planes that cause it to weather rapidly into flat blocks. One conical black hill, fifteen hundred feet high, is volcanic rock, close-grained and dense like some kinds of iron ore. ”

“ But in place of sharp-rimmed escarpments, and tors, and broken shattered ridges, we see everywhere a rounded and smoothly-flowing configuration which prevails up to a height of 1600 feet or thereabout, above which the rocks take on the rugged appearance which is natural to them. By what magic have the strata at the lower levels escaped in such large measure from the action of rain and frost, which have furrowed and shattered the higher mountain-tops? ”

“ The surface of the Earth is found to be covered with a series of irregular depressions or Basins, divided from one another, and sometimes wholly surrounded by projecting portions of subjacent strata, or by unstratified crystalline rocks, which have been raised into hills and mountains, of various degrees of height, direction and continuity. On either side of these more elevated regions, the strata dip with more or less inclination, towards the lower spaces between one mountain range and another. ”

“ It is a vast ocean of underground water, with mountains of water and valleys of water.
A great lake marks an underground soakage water level. A riverbed marks an underground seepage topography. The sea of water inside a continent is just as much a map of hills and dales of water as the land is a map of the hills and valleys of geography. The water is dynamic, it is flowing. The land surface is dynamic and rain fed; it is creeping soils. ”

“ The hills are shadows, and they flow
From form to form, and nothing stands;
They melt like mists, the solid lands,
Like clouds they shape themselves and go.
[F] This is the generally accepted view of modern geologists. It is very difficult, however, to understand how a wide continental area can be vertically upheaved. It seems more probable that the upheaval of the land is only apparent. The land seems to rise because the sea retreats as the result of the subsidence of the crust within the great oceanic basins. ”

“ On mountain sides, in ravines, and sea cliffs, the rocky masses of the earth are exhibited free from the obscurity of superficial accumulations: the industry of man, in mines, wells, roads, canals, has added to the facilities granted by nature, and from these opportunities the structure of the crust of the earth, the arrangement and relative position of the rocks, are known in the most essential points. ”

“ The entrance made by the waves is the record of a contest between the ocean and the granite, two equally powerful elements—one by its inertia, the other by its motion. The proof lies in some half-sunken rocks of fantastic shapes which prohibit the entrance of vessels. The hardy sons of the soil can in some places leap from rock to rock, undismayed by a gulf a hundred fathoms deep and six feet wide. ”

“ Other effects on topography.—Inequalities in the hardness of rock develop certain peculiarities of topography other than those of valleys. The less resistant portions of a land area more or less distant from streams are worn down more readily than those which are more resistant. If great areas of high land be capped with hard rock they are likely to remain as plateaus after surrounding areas of less resistance are brought low. ”

“ Should this sunken area be once more elevated en masse—pushed up bodily until it attains a height of several thousand feet—it will form a plateau, composed of a series of horizontal strata resting on the contorted and convoluted rocks of the ancient denuded mountain-chain. The surface of the plateau will now be traversed by streams and rivers, and in course of time it must become deeply cleft and furrowed, the ground between the various valleys rising into mountain-masses. Should the land remain stationary, its former fate shall again overtake it ”

“ It has often been noted with surprise that features of underground structure which, it might have been confidently anticipated, should have exercised a marked influence on the topography of the surface have not been able to resist the levelling action of the denuding agents, and do not now affect the surface at all. ”

“ If we can picture to ourselves the formation in those remote ages, that it is the geologist’s task to rehabilitate in thought, of a vast ridge, not sharp like the typical mountain range, but of broad dimensions like the swell of some vast ocean, we shall have the material then forming [4] the earth’s crust bent upwards, and in unelastic places broken, and this partly or entirely beneath the ocean. ”

“ The joints by which all rocks are traversed have been especially serviceable as dominant lines down which the rain has filtered, up which the springs have risen and into which the frost wedges have been driven. On the high bare scarps of a lofty mountain the inner structure of the mass is laid open, and there the system of joints even more than faults is seen to have determined the lines of crest, the vertical walls of cliff and precipice, the forms of buttress and recess, the position of cleft and chasm, the outline of spire and pinnacle. ”

“ A tremendous ascent among rocks and pines to a height of 9,000 feet brought us to a passage seven feet wide through a wall of rock, with an abrupt descent of 2,000 feet, and a yet higher ascent beyond. I never saw anything so strange as looking back. It was a single gigantic ridge which we had passed through, standing up knife-like, built up entirely of great brick-shaped masses of bright-red rock, piled one on another by Titans. ”

“ Where a new tract of land has been raised out of the sea by such an energetic movement as broke up the crust and produced the complicated structure and tumultuous external forms of a great mountain chain, the influence of the hypogene forces on the topography attains its highest development. But even the youngest existing chain has suffered so greatly from denudation that the aspect which it presented at the time of its uplift can only be dimly perceived. ”

“ In that age enormous Glaciers moved slowly downward from the snow-clad heights over innumerable valleys now rich with the fruits of the earth; ponderous Icebergs floated over wide areas of the ocean, where now the dry land appears; and vast piles of promiscuous rubbish, with great angular blocks of stone, were deposited 81 on the slopes and crests of submarine mountains that now tower hundreds of feet above the level of the sea. ”

“ From this period downward, the formations are all of more contracted dimensions, the basins narrowing in superficial area to the upper tertiaries, which partake of the character of local rather than of universal deposits; while the evidences here are innumerable that, until the globe settled into its present form, and assumed its present arrangement of seas, continents, and mountains, the land and water were continually changing places, the crust and framework subject to constant upheaval. ”

“ Fluviatile Deposits.
To discuss fully the origin and history of valleys, is an object reserved for a later section; we may now proceed to consider the effects produced, in valleys already formed, and partially filled with old detritus, by the water running therein. This is a large subject; for, besides the mechanical and chemical actions of the rivers and brooks, which vary according to the hardness and nature of the rocks, there is to be examined the influence of atmospheric vicissitudes, heat and cold, moisture, dryness, frost, &c. ”