462 SUPPLEMENTARY NOTES. 



Geol. Trans. Lond. N. S. Vol. II. p. 42. He also states that 

 the Purbeck series contains strata of Fresh-water origin, and is 

 thus distinguished from the Portland Oolite, which contains ma- 

 rine shells only. In the Paper referred to, he hesitates where to 

 draw the exact line of separation between these two formations, 

 but is inclined to place it at the Chert Bed, (See PI. 57, Fig. 1.) 

 an opinion which he still maintains. In the same Paper he con- 

 siders the Dirt Bed not to rest immediately upon a stratum of ma- 

 rine formation, (as Mr. De la Beche and myself have subsequently 

 and erroneously supposed it to do ; Geol. Trans. N. S. Vol. IV. 

 p. 15.) but that the Beds called Top Cap, immediately beneath the 

 Dirt Bed (see PI. 57, Fig. 1.) are of Fresh-water origin. Beneath 

 this Top Cap, two other seams of black earth of very small extent 

 and thickness, one about five feet and the other seven feet below 

 the Dirt Bed, were discovered in 1832, by Prof. Henslow, (Geol. 

 Trans. N. S. Vol. IV. p. 16,) and in the uppermost of these Dr. 

 Fitton has since found trunks of Cycadites, in the position which' 

 they would have occupied if they had grown there. (See GeoL. 

 Trans. N. S. V. iv. p. 219.) 



P. 375. In the course of the last year, Mr. Robert Brown has 

 ascertained by exmination of a Trunk of Cycadites microphyllus, 

 from Portland, the existence of scalariform vessels without discs, 

 in the mature Trunk ; a point in which he informs rae, these fos- 

 sils agree with the American portion of the order Cytadex, though, 

 in other repects, they bear a greater resemblance to the African and 

 Australian species. Mr. Brown observes farther, " that the order 

 Cycadese presents but one genus in America, namely, the ZamiOr 

 on which this genus was originally founded, and to which it has 

 been recently restricted ; and that the coincidence in the structure 

 of the scalariform vessels in the trunk of this Zamia of the New 

 World, with that of the fossil Cycadites of Europe, is very re- 

 markable," 



P. 38D. Note. Since the Publication of my first Edition, I 

 have been favoured with the following communication from Mr. 

 Bowerbank, respecting the fossil remains of vegetables found in 

 the London Clay, " I have, in my collection of fossil fruits from 



