The Story of a Boulder or, Gleanings from the Note-book of a Field Geologist

The Story of a Boulder; or, Gleanings from the Note-book of a Field Geologist

The present Volume has been written among the rocks which it seeks to describe, during the intervals of leisure of a field-geologist. Its composition has been carried on by snatches, often short and far apart, some of the descriptions having been jotted down on the spot by streamlet and hill-side, or in the quiet of old quarries; others, again, in railway-carriage or stage-coach. By much the larger portion, however, has been written by the village fireside, after the field-work of the day was overa season not the most favourable to any mental exercise, for weariness of body is apt to beget lassitude of mind. In short, were I to say that these Chapters have been as often thrown aside and resumed again as they contain paragraphs, the statement would probably not exceed the truth. But the erratic life of an itinerant student of science is attended with yet greater disadvantages. It entails an absence from all libraries, more especially scientific ones, and the number of works of reference admissible into his parva supellex must ever be few indeed. With these hindrances, can the writer venture to hope that what has thus been so disjointed and unconnected to him, will not seem equally so to his readers? Yet if his descriptions, written, as it were, face to face with Nature, - viii - are found to have caught some tinge of Nature's freshness, and please the reader well enough to set him in the way of becoming a geologist, he shall have accomplished all his design. It cannot be too widely known, or too often pressed on the attention, especially of the young, that a true acquaintance with science, so delightful to its possessors, is not to be acquired at second-hand. Text-books and manuals are valuable only so far as they supplement and direct our own observations. A man whose knowledge of Nature is derived solely from these sources, differs about as much from one who betakes himself to Nature herself, as a dusty, desiccated mummy does from a living man. You have the same bones and sinews in both; but in the one they are hard and dry, wholly incapable of action; in the other they are instinct with freshness and life. He who would know what physical science really is, must go out into the fields and learn it for himself: and whatever branch he may choose, he will not be long in discovering that a forenoon intelligently spent there must be deemed of far more worth than days and weeks passed among books. He sees the objects of his study with his own eyes, and not through "the spectacles of books;" facts come home to him with a vividness and reality they never can possess in the closet; the free buoyant air brightens his spirits and invigorates his mind, and he returns again to his desk or his workshop with a store of new health and pleasure and knowledge. Geology is peculiarly rich in these advantages, and lies in a manner open to all. No matter what may be the season of the year, it offers always some material for observation. In the depth of winter we have the effects of ice and frost to fall back upon, though the country should lie buried in snow; and then when the longer and - ix - brighter days of spring and summer come round, how easily may the hammer be buckled round the waist, and the student emerge from the dust of town into the joyous air of the country, for a few delightful hours among the rocks; or when autumn returns with its long anticipated holidays, and preparations are made for a scamper in some distant locality, hammer and note-book will not occupy much room in the portmanteau, and will certainly be found most entertaining company. The following pagesforming a digest of the Carboniferous rocksmay, perhaps, in some measure, guide the explorations of the observer, by indicating to him the scope of geological research, the principles on which the science rests, and the mode in which it is pursued. But I repeat, no book, no lecture-room, no museum, will make a geologist of him. He must away to the fields and study for himself, and the more he can learn there he will become the better geologist. He need not burden himself with accoutrements. A hammer, pretty stout in its dimensions, with a round blunt face and a flat sharp tail; a note-book and a good pocket-lens, are all he needs to begin with. Having these, let him seek to learn the general characters' of the more common rocks, aiding himself, where he can, by a comparison with the specimens of a museum, or, failing that, with the descriptions of a text-book. Let him then endeavour to become acquainted with some of the more characteristic fossils of the district in which he resides, so as to be able to recognise them wherever they occur. Private collections and local museums are now becoming comparatively common, and these, where accessible, will aid him vastly in his studies. Having at length mastered the more abundant rocks and organic remains of his neighbourhood, let him try to trace out - x - the connexion of the different strata across the country, so as to understand its structure. For this purpose it will be necessary to examine every ravine and natural exposure of the rocks, along with quarries, ditches, railway-cuttings, and, in short, the whole surface of the district. A general notion of the geology of the place will, not perhaps be of very difficult attainment; and this done, the observer should attempt to put down the connexion of the rocks on paper, for till this is accomplished he will have at the best but an imperfect, and perhaps incorrect notion of the subject. The best map of the district should be obtained, also a clinometer, or instrument for ascertaining the angle at which rocks dip with the horizon, and a pocket-compass with which to mark the direction of the dip and strike of strata, that is, the outcrop, or line which they form when they come to the surface. Thus armed, he may commence a geological survey of his neighbourhood. Wherever he sees a bed of rock exposed, it should be marked down on his map with an arrow pointing to the direction in which the stratum is dipping, the angle of dip, ascertained by the clinometer, being put alongside. The nature of the rock, whether sandstone, shale, limestone, or greenstone, must be set down at the same place, and, to save room, a system of marks for the different rocks may be conveniently used. When a sufficient area of ground has been thus traversed, the student may find, say a row of arrows on his map all pointing due west, and indicating a set of quarries about a quarter of a mile distant from one another, the rock in each of them dipping to the west. If there be at the one end a limestone containing certain fossils, and at the other end a stratum exactly similar, containing the same fossils, while the quarries between display the same rock, he will infer, of course, - xi - that the whole is one limestone, and will accordingly draw a line from the last quarry on the north to the last on the south, connecting them all together. If the bed dips steeply down, the line will be narrower,if but slightly inclined, it will be broader; the breadth of such a line (which may be coloured to taste) always varying with the thickness of the stratum and the angle which it makes with the horizon. In a district where faults and curvatures along with trap-rocks abound, the mapping becomes more complex, but the principle remains the samea curved stratum on the ground making a similarly curved band on the map, and a fault or dislocation of a set of beds producing, in the same way, a corresponding break in the lines traced. In short, a geological map should be as far as possible a transcript of the surface rocks of a country. The beginner should avoid, however, attempting too much; it will be enough for him at first to have mastered the leading features of the geology of his district; the details cannot be shown save on a map of a large scale, and are better transferred to his note-book. The use of such mapping is to enable us to gain a correct knowledge of the geological structure of a country, and of the relation of rocks to each other as regards age, origin, &c. Bacon tells us that "writing makes an exact man;" we may say with equal truth that mapping makes an exact geologist. It is sometimes easy enough to obtain a notion of the general character of a district by taking a few rambles across it; but we can never know it thoroughly until we have mapped it. And this is done not as mere dry routine, or by a series of hard uninteresting rules. In reading off the geological structure of a country, we ascertain its history during many thousand ages long prior to that of man. We become, as it were, - xii - interpreters of hieroglyphics, and historians of long-perished dynasties. ......Buy Now (To Read More)

Product details

Ebook Number: 66703
Author: Geikie, Archibald
Release Date: Nov 11, 2021
Format: eBook
Language: English