350 On the age of tire Coal strata in Central India. [No. 4, 



lias run through many successive changes of the earth's surface, 

 than the information they supply is not very precise. But the very 

 same may be said with greater force of the genus Terebratula in 

 the Fossil Fauna. And I have observed that, even among plants 

 of an undecided character as regards genus, there is generally some 

 form, which distinguishes the species of one epoch from those of 

 another. Besides, a geological age may be known from the abund- 

 ance of a genus or family of plants at one period as compared with 

 others. Though the discovery of a single species might not decide 

 the question, yet if the genus, to which it belongs, culminates in a 

 certain formation, and a particular stratum presents an unusually 

 large proportion of that genus, then some idea may be formed of 

 the age of that stratum. Such is the case with the entire fronded 

 ferns. They reached their maximum development in the Jurassic 

 period, as the Oolite of Scarborough, Stonesfield, and, according to 

 H. Miller's recent researches, of the North of Scotland, plainly 

 shows ; and one of them, the genus Tseniopteris, which is so fitly 

 associated in our carbonaceous strata with Glossopteris and Cyclop- 

 teris, is almost confined to the Oolite, there never having been an 

 example of it hitherto met with in the true coal measures. 



Having said thus much on the general principle, I proceed to 

 apply it to special instances. There are three localities with which 

 our strata admit of comparison — Stonesfield and Scarborough in 

 England, and Bichmond in Yirginia U. S. The slate at the former 

 British locality and the carbonaceous shales and sandstones at the 

 latter, are universally acknowledged, I believe, to be Lower Oolitic ; 

 while the American coal formation referred to, is generally assigned 

 to the same era. Now the connexion between our strata and the 

 Stonesfield slate seems to be, the abundance of Tceniopteris, and a 

 resemblance amoog the fruits or seeds. The similarity to Scarbo- 

 rough consists in the presence of what Lindley and Hutton call 

 Equisetum later ale with its deciduous discs at the joints of the 

 stem, a plant, which to the best of my knowledge has hitherto been 

 discovered nowhere else. The relation to Bichmond is more inti- 

 mate still, Tceniopteris magnifolia, found there by Prof. "W. B„ 

 Bogers, appears to be specifically identical with one of the same 

 genus here ; and the descriptions given of the Virginian Catamites 



