Geological map

“ The complete atlas will consist of several thousand folios, each of which contains a topographical and a geological map of a small section of country, and will be named after some well-known town or natural feature within the limits of the district named. The topographical maps will show the reliefs, drainage, and cultures of the districts, indicated by the usual or definite conventional marks. The geological maps will show on distinct sheets the areal geology, or the areas occupied by the various rocks of the district; the economical geology, or the distribution of useful minerals ”

“ The lines should preferably run across the long axis of an area, not parallel to it, and the predominating trend or general direction of the areas of one geologic formation on a map should decide the direction of the lines for all areas of that formation on the same map, even if the rule must be violated on some of the minor areas.
An effort should always be made to produce a pattern that is subordinate in strength to the main lines of the base map on which it is drawn. In black and white maps, as in colored maps, unlike patterns should be placed next to each other. ”

“ The conventional patterns used on a map to distinguish separate areas, chiefly geologic, are shown in Plate VIII. The patterns shown represent the proper combinations of lines, dots, and other forms and should be spaced openly or closely according to the size of the area covered, the contrast needed between areas, and the general clearness and effect desired. If a map is to show both small and large areas dense or closely spaced patterns should generally be used for the smaller areas, even if they may be required for some fairly large areas representing the same formation or condition. ”

“ If the geology be other than of the very simplest character—and this will generally be true of mountainous regions—it is not only necessary to fix the geographical positions of rock masses, but their elevations as well. In other words, the map must not only be a plan, but special elevations must be represented, known as geological sections. The most satisfactory representation—and this will be essential for all difficult areas—will be one which shows not only special elevations, but the topographic relief of every point in the area. ”

“ The great value of the modern topographical map is becoming, however, universally acknowledged, and every highly civilized nation has either completed or has in preparation sectional topographical maps of its domain on such a scale as is warranted by its financial condition and its state of development. Thus there is now being accumulated a vast library of geographical and to some extent geological information, of which the student of geology must be prepared to make use. ”

“ A finished map border is used or omitted according to the kind of map prepared. Diagrammatic maps and maps on which no parallels and meridians appear do not need finished borders. On a map that shows complete areal geologic or other coloring, such as a map in a Survey geologic folio, the border lines tend to destroy the simple effect of the whole map. On a map that is not completely colored and on all very large maps borders are really necessary. ”

“ The work in the future must be divided up among many persons, each doing a part; and Dr. Gray earnestly solicits the co-operation of all botanists.
The Proposed Geological Map of Europe.—The International Geological Congress, which met at Bologna last year, decided upon the preparation of a geological map of Europe, which should exemplify a uniform terminology and a uniform system of coloring, and appointed an International Committee to superintend the work. ”

“ In preparing an original geologic map a letter symbol, such as has been just described, or a number should be put in the proper place in the explanation, and the same symbol or number should be repeated at one or more places on the map within the areas to which it refers. Each area that is indicated by a color should be marked with the proper symbol in order to make its identification sure, for light colors especially are likely to fade and mixed colors can not be discriminated with certainty. ”

“ The degree of generalization in the geologic and other detail to be shown on a map usually involves a corresponding degree of generalization in its base. Absolutely true generalization means the same degree of omission of detail for each kind of feature. If a base map on a scale of 1 mile to 1 inch, prepared with the usual detail, were placed before a camera and reduced to a scale of 16 miles to 1 inch, the lines representing the smaller tributaries of streams and the smaller water bodies, as well as many other features, would probably be so greatly reduced in length as to be illegible. ”

“ Geological maps belong strictly to Descriptive Geology; they are free from those wide and doubtful speculations which form so large a portion of the earlier geological books. Yet even geological maps cannot be usefully or consistently constructed without considerable steps of classification and generalization. When, in our own time, geologists were become weary of controversies respecting theory, they applied themselves with extraordinary zeal to the construction of stratigraphical maps of various countries ”

“ It must be understood that the maps (A, B, C) are not meant to exhibit the geographical conditions of the world at any one point of time. In Map A, for example, the area coloured blue was not necessarily covered by sea at any particular stage in the Palæozoic era. It simply represents approximately the regions tended. But, as already stated, numerous oscillations of level occurred in Palæozoic times, so that many changes in the distribution of land and water must have taken place down to the close of the Permian period. ”

“ If a new map is to be compiled an accurate projection should first be constructed, and no plotting should be done on it until the projection has been checked and found to be correct. A projection should be checked or proved by some one other than the person who prepared it. Next the drainage and the water areas should be outlined; then the cultural features should be added; and finally the relief, whether expressed by contour lines, hachures, or shading. ”

“ Findings- Section 2 (a) of the National Geologic Mapping Act of 1992 (43 U.S.C. 31a (a) ) is amended— (1) by striking paragraph (1) and inserting the following: ` (1) although significant progress has been made in the production of geologic maps since the establishment of the national cooperative geologic mapping program in 1992, no modern, digital, geologic map exists for approximately 75 percent of the United States;' ”

“ As a conchologist he was held in high esteem, but while he recognized the similarity of fossil mollusca to living forms, he regarded them as inorganic imitations produced in the rocks. In 1683 he communicated to the Royal Society (Phil. Trans., 1684) , An ingenious proposal for a new sort of maps of countries; together with tables of sands and clays, such as are chiefly found in the north parts of England. In this essay he suggested the preparation of a soil or mineral map of the country, and thereby is justly credited with being the first to realize the importance of a geological survey. ”

“ Anyone who attempts to draw a base map must, first of all, know how each feature or part of the map should be represented. Most of the conventional symbols for features shown on base maps are well established and should invariably be used; for instance, a line composed of alternate long and short dashes (not dashes and dots) represents a county boundary, and a line or two parallel lines across which short lines are drawn at regular intervals represents a railroad. ”

“ In the case of the Ordnance Survey map, on the scale of 1 inch to a mile, the varying forms of the surface are so faithfully delineated as frequently to indicate to a trained observer the nature of the rocks and the geological structure of the ground. ”

“ These publications are illustrated with well-selected half-tones and carefully prepared black and white maps based on the accurate topographic maps issued by the Geological Survey.
The first need of the intelligent traveler is a map of the area he is about to traverse. Fortunately excellent maps of almost all the larger parks are for sale by the United States Geological Survey at nominal prices. Maps have been published of Yellowstone, Yosemite and Glacier national parks on a scale of 2 miles to the inch ”

“ Study a good map—a quadrangle of the U. S. Geological Survey, for instance. Note what things are represented, and how representation is made: study the map, until it is thoroughly understood.
There are three factors with which the map-maker deals: direction, distance, and elevation. With the first, he must always reckon, and usually with the second and the third as well.
Direction is fundamental. Suppose there are three dominant points in the area to be mapped, relatively situated as here indicated. ”

“ In the geological maps, regard should be had to various questions which deserve the special consideration of the Congress, such as the scales best adapted for different purposes, the colors and symbols to be used, and the proper mode of representing superficial deposits conjointly with the underlying formations. ”

“ By C. A. Süssmilch, F.G.S. Second edition, thoroughly revised and greatly enlarged, with folding coloured map and 100 other maps and illustrations. Cloth gilt, 7s. 6d. (postage 3d.) Australian Mining Standard: "Students are greatly indebted to Mr. Süssmilch for the able manner in which he has presented in compact form all that is known at the present time on the subject.... The illustrations throughout are excellent, but the coloured geological map which serves as a frontispiece is a model of what such a map should be, avoiding the opposite evils of overcrowding and meagreness. Mr. ”

“ These relations of position required that geological maps, to complete the information they conveyed, should be accompanied by geological Sections, or imaginary representations of the order and mode of superpositions, as well as of the superficial extent of the strata, as in more recent times has usually been done. The strata, as we travel from the higher to the lower, come from under each other into view ”

“ Hidden under the farm vegetation or masked by the woods are scattered outcroppings of rock which have been the basis of the geologist’s judgment in preparing the map. Experience shows that in order to bridge the wide gap between the geology in the landscape and the patches of color upon the map something more than mere examination of the colored sheet is necessary. ”

“ In this work the British hydrographic office may justly claim the credit of having contributed the chief share. Great Britain has likewise taken the lead in those deep-sea explorations which reveal to us the configuration of the sea-bottom, and enable us to construct charts of the ocean bed corresponding to the contoured maps of dry land yielded by topographical surveys. (E. G. R.)
Map Projections In the construction of maps, one has to consider how a portion of spherical surface, or a configuration traced on a sphere, can be represented on a plane. ”

“ For a long time mountains were supposed to be the limitations of rivers, and old maps represent them always as flowing along the valleys without ever passing through the mountain-chains that divide them; but geology is fast correcting the errors of geography, and a map which represents merely the external features of a country, without reference to their structural relations, is no longer of any scientific value. ”

“ What the ideal geographer, as cartographer, first of all tries to do is to devise a notation by which he and his fellow-geographers, by the inspection of a map of a given region, may get a simultaneous vision of the terrestrial phenomena which all the explorers and observers of that region have collectively seen. Now it must always be that however minutely observed and explored a region—even the most inhabited—may be, there is always something new to be observed, even in the shape and configuration of the surface, for these are always changing ”

“ Commercial considerations are not to be overlooked; cheap and rapid methods of reproduction bring their temptations as well as their advantages to bear upon cartography. Their advantages are manifest; the map, whether as an adjunct to travel or as a graphic illustration of a great variety of subjects, has become a commodity of almost daily use. But in some countries, such as the United States, the standard of cartography generally is as low as that of the maps of the survey is high. ”

“ On seeing a relief map of one of the continents for the first time, there arises a sense of wonder and surprise, and as the realization dawns upon one of the continuity of the great mass of land represented, with its altitudes and depressions, and that it is one stupendous aggregation of soil, rock and vegetation, surrounded by a great expanse of water, a feeling of awe and astonishment is awakened. ”

“ Without the aid of Geology the geographer cannot, in fact, discriminate between mountains of elevation and mountains of denudation; hence geographical terms so constantly in use as mountain-range and mountain-chain are very often applied by writers, ignorant of geological structure, to elevated regions which have no claim to be described either as chains or ranges. Some knowledge of Geology, therefore, is essential to us if we would have correct views of many of the grandest features of the globe. ”

“ When dealing with maps not drawn on an equal area projection we substitute quadrilaterals bounded by meridians and parallels, the areas for which are given in the “Smithsonian Geographical Tables” (1894) , in Professor H. Wagner’s tables in the geographical Jahrbuch, or similar works.
It is obvious that the area of a group of mountains projected on a horizontal plane, such as is presented by a map, must differ widely from the area of the superficies or physical surface of those mountains exposed to the air. Thus, a slope of 45° having a surface of 100 sq. m. ”