Memoirs of the Museum of Comparative Zoology at Harvard College Volume 6

Memoirs of the Museum of Comparative Zoology at Harvard College Volume 6

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1880 edition. Excerpt: ...substance, apparently almost entirely made up of rhyolitic ash. The same is the case in the well-known "fossil forest" near Calistoga, in the Coast See ante, pp. 235-239. Ranges. It would appear that the wood has been best preserved when surrounded by eruptive materials, in which the trees may perhaps have grown, or which may have been swept over the trunks, after they had been prostrated by age or other causes, so as entirely to envelop them. Many fragments of silicified wood are found in the coarse gravel; these, however, usually have a more or less water-worn appearance, and may have been carried by currents of water far from the place in which they grew. The lava itself frequently exhibits signs of having been acted on by silicifying agents after its deposition. Some of the beds of white ashes have evidently undergone a change since they reached the place where they now lie; the whole mass, which, in all probability, was originally light and incoherent, has acquired more or less completely the texture and appearance of semi-opal, as if acted on by silicifying waters. The abundance of infusorial silica in portions of the volcanic rocks occurring in close connection with the gravels, as already described, is another proof of the frequent presence of this element in such condition that it could be readily assimilated by the organisms requiring it for their development. The legitimate inference, then, from what has been stated above, is that a large part if not the whole of the series of beds included within the gravel formation has been at some period since its deposition quite thoroughly permeated with water holding silica in solution in sufficient quantity and in the right condition to bring about extensive chemical changes...show more

Product details

  • Paperback | 364 pages
  • 189 x 246 x 19mm | 649g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236846141
  • 9781236846143