Boulangerite

( Min.) A sulphuret of lead and Boul'der, Bowl'der, n. [From BOWL.] A smooth, round stone, such as is found on the sea-shore; a large pebble. ( Geol . ) A fragment of rock rounded by attrition, lying on or within the surface, and not derived from the rocks on which they lie. In many cases these B. have been transported hundreds of miles, and sometimes only a few yards; but they have always been moved from their original position by the action of water or ice. A boulder of granite, 42 ft. long. 27 ft. broad, and 21 ft. high, has been used as a plinth of the statue of Peter the Great at St. Petersburg. Small B. of foreign rocks have been found in chalk and other aqueous rocks. Boul'der, a. Belonging to, or consisting of, boulders. Boul'der, in Colorado , a Northern county, bounded on the W. by the Rocky Mountains, and traversed by Boulder Creek. Area , about 600 sq. m. Soil , productive, and with many gold and iron mines yielding a fair amount of ore. Cap . Boulder City. BOULDER CITY, a thriving city of Col .; cap. of ab. co., 45 m. from Denver, and the terminus of several R. R. The State University is at B. Boulder, in low a , a twp. of Lynn co. Boulder Clay, n. (Geol.) A deposit, often very extensive, consisting of boulders of various size, angular or rounded, mixed with sand and clay, and lying generally in an unstratified position unconformably to the other rocks on the earth's surface. Although there is no reason why such a deposit should not have been made at any geological period, B. C. seems to be of definite age in the northern hemisphere, or at least is limited to a certain geological period. It is one of those deposits spoken of collectively, as Drift , and would seem to be due to a time not very distant, when glaciers covered much of north European land, and icebergs drifted, and were stranded over the shoals that have since been raised to form the land. - See GLACIAL DRIFT. Boul'der Creek, in Montana , a branch of the Madison fork of the Mi ouri river, taking a N.W. course. Boul'der Valley, in Montana , the capital of JefferBoulder-wall, n. A wall built up of large stones or son co. boulders.