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OEOK TEPE 284 GEOLOGY passage round the Cape of Good Hope and that of America in the 16th century gave a great impulse to its modern ad- vance. In the United States geograph- ical science has been carefully fostered by the government, a board being ap- pointed to supervise all practical work and to insure uniformity of nomencla- ture. Under the patronage of several of the earlier presidents, there was great activity in geographical research and ex- ploration of the vast domain which lay to the W. of the then settled portions of the country. The most notable of these early expeditions was that undertaken by authority of President Jefferson, the leaders of the enterprise being Gen. Meriwether Lewis and Gen. William Clark (afterward governor of the ter- ritory of Louisiana). This attempt bore- fruit in the settlement of the great Mississippi basin to the N. W., and it was supplemented a few years after by the expedition under Lieut, (afterward Gen.) John C. Fremont. The great apostle of the United States Coast Survey was Ferdinand Rudolph Hassler, who was invited to the United States by President Tyler. A gieographical congress was held at Paris in 1875, and at the Columbian Exposition in Chicago. GEOK TEPE, a town and fortress of central Asia, oasis of the Akhal-Tekke- Turkomans, Ion. 58° E., lat. 38° N. In 1879 the Russians under General Lo- makine were defeated here with heavy loss, but January, 1881, it was stormed by General Skobeleff after a three weeks' siege, when about 8,000 fugitives were massacred, no quarter being given. GEOLOGICAL SURVEY, UNITED STATES, a bureau of the Interior De- partment created for the purpose of preparing a map of the United States, classifying the public land, examining the geological structure, mineral resources, and the products of the country. To these duties have since been added those of investigating the extent to which the arid lands of the West can be redeemed by irrigation, segregating the irrigable from the non-irrigable lands, and the selection of sites for reser- voirs and canals for the purposes of irrigation. The maps made by the Geo- logical Survey are all on a large scale, and have a ♦degree of accuracy and a minuteness in detail incomparably great- er than ordinary maps. The smallest scale is 1-250,000, or about 4 miles to the inch, and this scale has been employed for regions of the West which are thinly settled, and where the topography is mountainous. But it has been super- seded by scales of 2 miles and 1 mile to the inch, the latter for populous regions with slightly or moderately diversified topography, like Massachusetts and New Jersey. The maps are engraved on sheets which, with the 4-mile scale, em- brace 1° of lat. and 1° of Ion. The 2-mile maps embrace tracts of half the above linear or one-fourth the areal di- mensions; the 1-mile maps embrace one- fourth of the above linear and one-six- teenth the areal dimensions. The topog- raphy is represented by "contours" or "grade curves"; i. e., by lines of equal al- titude above the sea. The contour inter- vals are uniform for each sheet, but vary in different sheets acording to the charac- ter of the country. In some tracts the contour intervals represent a difference of elevation of 200 feet, these being in very mountainous countries, while in flat countries and on large-scale sheets they may be as small as 20 feet. The general construction and methods of all maps are, however, the same. There are three principal branches of the geological survey: (1) Geology prop- er; (2) Topography; (3) Irrigation sur- veys. The geological branch investigates the stratigraphy, the geological struc- ture and history, the lithology, mineral- ogy, and palaeontology, the ores and mines, and in general the natural eco- nomics, resources, and physical geog- raphy of the country. The topographic branch prepares the maps ; the irrigation branch investigates the possibilities of irrigation and selects the irrigable lands and sites available for reservoirs and canals. The work of the topographic branch is the basis of the work of the other two, and all the results of the latter are projected on the maps. The publications of the Survey are (1) the annual report of the director, which, be- sides the administrative report, contains memoirs on geologic subjects by mem- bers of the survey, and is distributed according to the regulations of the In- terior Department; (2) monographs on the leading subjects of special investi- gation by the geologists; (3) bulletins on more limited special subjects of re- search; (4) an annual volume of mineral statistics. The last three are distributed gratuitously only to designated libraries and to learned corporate societies, which send their own publications in exchange. Otherwise they are sold by the director at 10 per cent, above the cost of publica- tion, and the money deposited in the Treasury. GEOLOGY, the science which investi" gates the bygone history of the earth with the view of accounting for its pres- ent condition. It is the province of physical and political geography to de-