Discourses : biological & geological : essays / by Thomas H. Huxley.

  • Huxley Thomas Henry, 1825-1895.
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: Discourses : biological & geological : essays / by Thomas H. Huxley. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    G I carbonate of lime. Tlie crust wliidi is often deposited by waters wliicli liave drained tbrough limestone rocks, in the form of what are called stalagmites and stalactites, is carbonate of lime. Or, to take a more familiar exam]3le, the fur on the inside of a tea-kettle is carbonate of lime; and, for anything chemistry tells us to the con- tiary, the chalk might be a kind of gigantic fur upon the bottom of the earth-kettle, which is kept pretty hot below. Let us try another method of making the chalk tell us its own history. To the unassisted eye chalk looks simply hke a very loose and open kind of stone. But it is possible to grind a slice of chalk down so thin that you can see through it until it is thin enough, in fact, to be examined with any magnifying power that may be thought desirable. A thin slice of the fur of a kettle might be made in the same way. If it were examined microscopically, it would show itself to be a more or less distinctly laminated mineral sub- stance, and nothing more. But the slice of chalk presents a totally different appearance when placed under the inicroscoj^e. The general mass of it is made up of very minute granules; but, imbedded in this matrix, are in- numerable bodies, some smaller and some larger, but, on a rough average, not more than a hundredth of an inch in diameter, having a well- defined shape and structure. A cubic inch of