. Elements of geology. Geology. PART L CHAPTER III. 39 Infusoria in TripoJi. men is now converted into a stony mass, a mixture of clay and lime; but it must once have been buoyant and floating in the sea, when the Teredinse lived upon it, perforating it in all directions. Again, before the infant colony settled upon the drift wood, the branch of a tree must have been floated down to the sea by a river, uprooted, perhaps, by a flood, or torn off* and cast into the waves by wind; and thus our thoughts are carried back to a prior period, when the tree grew for j^ears on dry land, enjoying a fit s
. Elements of geology. Geology. PART L CHAPTER III. 39 Infusoria in TripoJi. men is now converted into a stony mass, a mixture of clay and lime; but it must once have been buoyant and floating in the sea, when the Teredinse lived upon it, perforating it in all directions. Again, before the infant colony settled upon the drift wood, the branch of a tree must have been floated down to the sea by a river, uprooted, perhaps, by a flood, or torn off* and cast into the waves by wind; and thus our thoughts are carried back to a prior period, when the tree grew for j^ears on dry land, enjoying a fit soil and climate. It has been already remarked that there are rocks in the inte- rior of continents, at various depths in the earth, and at great heights above the sea, almost entirely made up of the remains of zoophytes and testacea. Such masses may be compared to modern oyster-beds and coral reefs; and, like them, the rate of increase must have been extremely gradual. But there are a variety of stony deposits in the earth's crust now proved to have been derived from plants and animals of which the organic ori- gin was not suspected until of late years, even by naturalists. Great surprise was therefore created by the recent discovery of Professor Ehrenberg of Berlin, that a certain kind of siliceous stone, called tripoli, was entirely composed of millions of the skeletons or cases of microscopic animalcules. The substance alluded to has long been well known in the arts, being used in the form of powder for polishing stones and metals. It has been procured, among other places, from Bilin, in Bohemia, where a single stratum, extending over a wide area, is no less than 14 feet thick. This stone, when examined with a powerful micro- scope, is found to consist of the siliceous cases of infusoria, united together without any visible cement. It is diflicult to convey an Fig, 14. Fig. 15. Fig. Bacillaria Oaillonella Oaillonella vulgaris ? distans. ferruginea. These figures are mag
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Keywords: ., bookauthorlyellcharlessir17, bookcentury1800, booksubjectgeology
