An elementary treatise on mineralogy and geology: designed for the use of pupils : for persons, attending lectures on these subjects : and as a companion for travellers in the United States of America, Volume 2

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Cummings and Hilliard, 1822 - Geology - 5 pages
 

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Page 48 - When a ray of light passes obliquely from one medium to another of different density, it is refracted or bent out of its course.
Page 187 - Marl, like clay, belongs both to secondary and alluvial earths, where it occurs in masses or in beds. Hence it is found associated with compact limestone, chalk, gypsum, or with sand or clay. It contains various organic remains, as shells, fish, bones of birds and of quadrupeds, and sometimes vegetables.
Page 622 - The heliotrope has formed among it in centres, to which the chalcedony seems to have been drawn, as if by molecular attraction. We find a mass, varying from the size of a walnut to that of a man's head, occupying some larger vesicle or crevice of the amygdaloid, and all the smaller vesicles around it, for an inch or two, filled with what we may venture to term satellite heliotropes, some of them as minute as grains of wild mustard, and all of them more or less earthy, generally in proportion to their...
Page 770 - ... as to admit the passage of water. Sometimes, indeed, this rock is vesicular. Some varieties are so solid as to give fire with steel, while others are friable, and may be reduced to powder even by the fingers. Its fracture is always granular or earthy, although it may be at the same time conchoidal or splintery.
Page 67 - THE specific gravity of a body is its weight compared with that of another body of the same magnitude.
Page 188 - ... of the earths which it contains ; and whether a calcareous or an argillaceous marl will be more suitable to a given soil, may be determined with much probability by its tenacity or looseness, moisture or dryness. To employ marls judiciously, therefore, the farmer should be in some degree arquainted with the chemical properties or constituent parts of the marl itself, and with the ingredients of the soil.
Page 671 - ... than the calamine. Sheet zinc is becoming an article of considerable demand in the market, for culinary purposes, and as a covering for valuable buildings, instead of lead. But the chief consumption of this metal is in making brass, well known to be a compound of copper and zinc. In this process, the carbonate of zinc, previously calcined, is mixed with charcoal and granulated copper, and then exposed to a suitable heat. The common brass imported from England contains upwards of thirteen per...
Page 775 - All true conglomerates must of course be composed of fragments of previously existing rocks. They have, however, been formed at very different periods. A breccia is an aggregate of angular fragments of the same mineral, or of different minerals, united by some cement. Sometimes, however, a few of the fragments are a little rounded. SANDWICH ISLANDS ; a cluster of islands in the North Pacific ocean, discovered by captains Cook and King in 1778, who gave them their present name in honor of the first...
Page 187 - Earthy mart differs from the preceding by being more or less friable, or even loose ; but they gradually pass into each other. Like the indurated marl, it may be either calcareous or argillaceous. It sometimes greatly resembles clay, but may be distinguished by its effervescence in acids.
Page 425 - At first small gray specks or elevated gray spots (glanders-nodules), varying in size from that of a pin's head to that of a pea, make their appearance (Fig.

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