1872.] MEYER— WEALDEI^ xVND " PUj^TEIELD EOEMAIIO:^." 243 



On the AVEALDEiir as a FLUVio-iACtrsxKiNE Foemation, and on the 

 eelation of the so-called " Pttnfield Foemation " to the Wealdei^ 

 and NEOcoiiiAK. By C. J. A. Meyer, Esq., F.G.S. 



Amongst the suggestions which, have from time to time been 

 offered in explanation of the origin of the Wealden strata of the 

 south-east of England, the one which has hitherto obtained the 

 most favour amongst geologists is that of their accumulation as the 

 delta of some great river open to the sea. 



That these strata are mainly of fluviatile origin can hardly be 

 doubted ; that they formed the delta of a single river is not so cer- 

 tain ; and with respect to their mode of accumulation, it is at least 

 open to question whether they do not represent, as a whole, a lacus- 

 trine rather than an estuarine deposit. 



It may seem at first sight of little consequence which of these 

 views is held to be correct. I shall attempt to show, however, that 

 the question is one of real importance, not only as regards the his- 

 tory of the Wealden strata themselves, but with respect also to the 

 relation of the Wealden beds to certain Neocomian strata with which 

 they were, no doubt, in part coeval. 



To the fluvio-lacustrine origin of the Wealden strata which I 

 propose to advocate, many objections may of course be raised ; but 

 these I shall not anticipate, the objections to their purely fluviatile 

 or estuarine origin appearing to me to be of greater weight. The 

 exceedingly quiet deposition of much of the sedimentary strata, the 

 almost total absence of shingle, the prevalence, both numerically and 

 specifically, of such species of mollusca as delight most in quiet 

 waters, the comparative absence throughout the greater portion of 

 the series of broken shells such as always abound in tidal rivers, 

 and, I believe I may say also, the total alssence of any trace of drift 

 wood perforated by mollusca in either the Purbeck or Wealden strata, 

 all seem to me to point to the same conclusion — namely, to the accu- 

 mulation of such strata beneath the waters of a Avide but shallow 

 lake, whose superfluous waters during the middle Wealden era es- 

 caped, indeed, to the sea, but only by some narrow outlet*, and 

 whose area was perhaps occasionally, though rarely, invaded by the 

 ocean. 



It is not my purpose to define the boundary of such lake, the out- 

 line of the land-surface of the- period, or even the source or bearing 

 of its rivers. The most I will now venture to suggest is this — that 

 the country of Western Europe at the time of the deposition of the 

 Wealden was not simply, as has been often suioposed, a land traversed 

 by some great river " laden with spoils from a distance," but that 

 such land held within itself at once the origin and point or points of 

 outfall of the V/ealden rivers. 



There is probably no fact in the past physical history of Europe 

 more generally admitted by geologists than that of the steady in- 

 crease of land towards and at the close of the Oolitic period. Such 



* It is more than pi'obable that the waters of the Piu'beckand ^afcr Wealden 

 period had no outlet whatever to the ocean. 



