. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. chemical deposits in veins. 775 slid to the right, we obtain considerable variation in the cavities so produced, two long irregular open spaces, //, fig. 768, being then formed. This wiU serve to show to what slight circumstances con- siderable variations in the character of the openings between unevenly fractured surfaces may be due, such surfaces being moved upon each other, so as to have numerous points of contact. Most lodes are perpendicular to the
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. chemical deposits in veins. 775 slid to the right, we obtain considerable variation in the cavities so produced, two long irregular open spaces, //, fig. 768, being then formed. This wiU serve to show to what slight circumstances con- siderable variations in the character of the openings between unevenly fractured surfaces may be due, such surfaces being moved upon each other, so as to have numerous points of contact. Most lodes are perpendicular to the horizon, or nearly so; but some of them have a considerable inclination or " hade," as it is termed, the angles of dip varying from 15° to 45°. The course of a vein is frequently very straight; but if tortuous, it is found to be choked up with clay, stones, and pebbles, at points where it departs most widely from verticality. Hence at places, such as a, fig. 769, the miner com- plains that the ores are " nipped," or greatly reduced in quantity, the space for their free deposition having Fi£ 769- been interfered with in consequence of the preoccu- pancy of the lode by earthy materials. When lodes are many fathoms wide, they are usually filled for the most part with earthy matter, and fragments of rock, through which the ores are much disseminated. The metallic substances frequently coat or encircle detached pieces of rock, which our miners call "horses" or "; That we should find some mineral veins which split into branches is also natural, for we observe the same in regard to open fissures. Chemical Deposits in Veins.—If we now turn from the mechanical to the chemical agencies which have been instrumental in the produc- tion of mineral veins, it may be remarked that those parts of fissures which were not choked up with the ruins of fractured rocks must always have been filled with water; and almost every vein has prob- ably be
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
