. The prospector's field-book and guide in the search for and the easy determination of ores and other useful minerals. on the sides of a mountain in a direction nearlyparallel with the valleys contain more extensivedeposits of lead than those which cross the valleysat right angles.* The prospector should keep this suggestion inmind. The lead ores are found in the fissures where theyseem to have been deposited by waters which havedissolved them out from neighboring beds (Fig. 56). In the United States the chief sources of lead inlate years have been argentiferous ores and consid-erable from zi
. The prospector's field-book and guide in the search for and the easy determination of ores and other useful minerals. on the sides of a mountain in a direction nearlyparallel with the valleys contain more extensivedeposits of lead than those which cross the valleysat right angles.* The prospector should keep this suggestion inmind. The lead ores are found in the fissures where theyseem to have been deposited by waters which havedissolved them out from neighboring beds (Fig. 56). In the United States the chief sources of lead inlate years have been argentiferous ores and consid-erable from zinc ores, but a notable exception is * British Mining, by Kobert Hunt, London, 1884, p. 344. LEAD AND TIN. 181 S. E. Missouri, where galena accompanied by nickel-iferous pyrite is disseminated through magnesianlimestone of Cambrian age. The mines are atBonne Terre, Mine la Motte and Doe Run. Thestrata lie almost horizontal, and are known to carrylead through over 300 feet in thickness. II. Tin. When a tin-bearing mineral is heated. Section op a Lead Deposit in a Fissure of the Limestone. Williams & Mine, Wisconsin. B, B, B, B, limestone. A, the fissure running , C, C, C, masses of ore. Metamorphic. before the blow-pipe with carbonate of soda or char-coal, white metallic tin is yielded. By dissolvingthis in hydrochloric acid and adding metallic zinc,the tin will be deposited in a spongy form. In theblow-pipe assay tin leaves behind a white depositwhich cannot be driven off in either flame. If itbe moistened with nitrate of cobalt solution, thedeposit becomes bluish-green, and this test distin-guishes it from other metals. Assay of tin ore. If the ore is poor it should beconcentrated, the vein-stuff being got rid of as much 182 prospectors field-book and guide. as possible. If mixed with iron or copper pyrites,it should be calcined or else treated with method is to mix the ore with one-fifth of itsweight of anthracite coal or charcoal, and expose itin a crucibl
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