FOSSIL PLANTS AS AN AID TO GEOLOGY. 177 



the most important industries. In this district there are a num- 

 ber 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 distin- 

 guished 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 Besseges, 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 Gangieres, but he also found that between 

 the beds of Besseges and Gangieres 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 



