Ch. XVni.] LOWER CRETACEOUS AND WEALDEN FLORA. 265 



species of shells, such as now inhabit Louisiana, has been upraised, and 

 made to occupy a wide geographical area, while a newer delta is form- 

 ing ;* and the possibility of such movements, and their effects, must not 

 be lost sight of when we speculate on the origin of the Wealden. 



If it be asked where the continent was placed from the ruins of which 

 the Wealden strata were derived, and by the drainage of which a great 

 river was fed, we are half tempted to speculate on the former existence of 

 the Atlantis of Plato. The story of the submergence of an ancient conti- 

 nent, however fabulous in history, must have been true again and again 

 as a geological event. 



The real difBculty consists in the persistence of a large hydrographical 

 basin, from whence a great body of fresh water was poured into the sea, 

 precisely at a period when the neighboring area of the Wealden was 

 gradually going downwards 1000 feet or more perpendicularly. If the 

 adjoining land participated in the movemient, how could it escape being 

 submerged, or how could it retain its size and altitude so as to continue 

 to be the source of such an inexhaustible supply of freshwater and sedi- 

 ment ? In answer to this question, we are fairly entitled to suggest that the 

 neighboring land may have been stationary, or may even have undergone 

 a contemporaneous slow upheaval. There may have been an ascending 

 movement in one region, and a descending one in a contiguous parallel 

 zone of country ; just as the northern part of Scandinavia is now rising, 

 while the middle portion (that south of Stockholm) is unmoved, and the 

 southern extremity in Scania is sinking, or at least has sunk within the 

 historical period.f We must, nevertheless, conclude, if we adopt the 

 above hypothesis, that the depression of the land became general through- 

 out a large part of Europe at the close of the Wealden period, and this 

 subsidence brought in the cretaceous ocean. 



FLORA OF THE LOWER CRETACEOUS AND WEALDEN PERIOD. 



The terrestrial plants of the Upper Cretaceous epoch are but little 

 known, as might be expected, since the rocks are of purely marine origin, 

 formed for the most part far from land. But the Lower Cretaceous or 

 Neocomian vegetation, including that of the AVeald Clay and Hastings 

 Sands, is by no means scanty. M. Adolphe Brongniart, when dividing 

 the whole fossiliferous series into three groups in reference solely to fossil 

 plants, has named the primary strata " the age of acrogens ;" the second- 

 ary, exclusive of the cretaceous, " the age of gymnogens ;" and the third, 

 comprising the cretaceous and tertiary, " the age of angiosperms."J He 

 considers the lower cretaceous flora as displaying a transitional character 

 from that of a secondary to that of a tertiary vegetation, Coniferce and 

 CycadecE (or Gymnogens) still flourished, as in the preceding oolitic and 



* See above, p. 84 ; and Second Visit to the U. S. vol. ii. chap, xxxiv. 



f See the Author's Annivers. Address, Geol. Soc. 1850, Quart. Geol. Journ. voL 

 \i. p. 52. 



:|: la this and subsequent remarks on fossil plants I shall often use Dr. Lind- 

 ley's terms, as most familiar in this country ; but as those of M. A. Brongniart are 



