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FOSSIL PLANTS AS AN AID TO GEOLOGY.
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the most important industries. In this district there are a number of veins of workable coal which have been formed at different epochs. These veins are separated from each other by barren strata of varying thickness, and are always accompanied by certain characteristic plants, especially ferns and allied forms.

In the valley of the Grand' Combe there are a number of coal openings, among which may be more especially distinguished those of the Sainte Barbe and Grand' Combe. M. Zeiller, the engineer-in-chief of the mines, from a study of the fossil plants which accompany the two layers, determined that the first deposit, viz.: that of Sainte Barbe, was older than the other. With this knowledge in his possession, M. Zeiller did not hesitate to counsel the company that by sinking a shaft at a place called Richard, just outside of the valley of the Grand' Combe, they would reach a new seam of coal corresponding to the Sainte Barbe. The shaft was sunk for 400 meters, but as only barren strata were encountered it was abandoned, and it was reserved for Grand' Eury to prove the correctness of Zeiller's prediction.

Grand' Eury, in a general study of the coal basin of Gard by means of fossil plants, determined that the coal of Sainte Barbe was deposited at the same epoch as that of Bessèges, from the fact that the same plants occurred at both localities. In the same manner he proved that the coal of Grand' Combe was of the same age as that of Gangières, but he also found that between the beds of Bessèges and Gangières there was a barren series of strata approximating 600 meters in thickness. It therefore became evident that the shaft at Richard had been abandoned too hastily, and work was again prosecuted, and at a depth of 731 meters the vein of coal, 4.80 meters thick, corresponding to the Sainte Barbe, was reached.

Study of fossil plants by means of internal structure.

By far the larger proportion of fossil plants are preserved in the form of impressions or casts of leaves, fruits, stems, etc., only comparatively few having the internal structure so preserved as

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