Ch. 7: Quartz Group - Opal, Rock Crystals, Amethysts, Rose Quartz, Agate, etc.

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	140	GEMS AND PRECIOUS STONES IN THE

	indurated clays, and moderately coarse conglomerate, and contained many vegetable remains, such as branches, rootlets, fruits, and leaves. In the stratum of sandstone occupying the horizon, nearly on a level with the present top of the giant tree, there was a large variety of most perfectly preserved leaves, specimens of which were determined by Leo Lesquereux to belong to the lower Pliocene or upper Miocene, and similar to the Chalk Bluff, Cal., specimens of Prof. Josiah D. Whitney. At a point about a mile further east, trunks and fragments of trunks were found in great numbers and in all conceivable positions. In most cases the woody structure was well preserved, but the trunks had a tendency to break in sections, and on the exposed ends the lines of growth from center to circumference could be counted with ease. In many cases the wood was completely opalized or agatized, and cavities existing in the decayed trunks were filled with crystals of quartz and calcite. Nearly all of the crystals found in the West have been formed in the hollow of silicified trees, notably in the case of the smoky quartz found in the Pike's Peak Region in Colorado. Gen. William T. Sherman, while visiting Fort Wingate, N. M., during his trip across the continent, in the autumn of 1878, suggested to the officer in charge of that post the desirability of securing several large trunks of these fossil trees, found in that vicinity, for the United States National Museum. In the following spring an expedition was sent out for this purpose, under the direction of Lieut. J. T. C. Hegewald, who states that in the locality of Litho-dendron Valley, where they were procured, the soil was composed chiefly of clay and sand, and the petrified wood, broken into millions of pieces, lay scattered around the slopes of the valley. Some of the large fossil trees were well preserved, though the alternate action of heat and cold had broken most of them in sections from 2 to 10 feet long, and certain of these he regarded as having been immense trees. On measuring the exposed parts of several, it was found that they varied from 150 to 200 feet in length and from 2 to 4 1/2 feet in diameter, and their centers often contained beautiful quartz crystals. A microscopic examination shows the internal structure of all to have been tolerably well preserved, the cells having suffered but little from

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