Geological Society of London. 283 



Wealden strata of tlie south-east of England. From the sequence 

 of the strata, no less than on palseontological evidence, he considered 

 the whole of the so-called " Punfield formation " of the Isle of 

 Purbeck to be referable to the Lower Greensand of the Atherfield 

 section. 



Discussion. — Mr, Godwiu-Austen did not agree with Mr. Judd in calling the 

 bed at Punfield the Punfield " formation ; " it was merely a bed intercalated between 

 beds of a different character below and above. There could be no doubt of the 

 "Wealden deposits extending over an area at least equal in extent to many of the 

 freshwater lakes at present in existence ; and the freshwater conditions exhibited by 

 the Wealden must have been in existence during an immense length of time. At 

 Punfield alone, however, was there evidence of the transition from freshwater to 

 marine conditions, as the other reputed cases seem to be merely instances of landslips. 

 The change from one condition to the other might, he thought, be due to a very 

 slight depression. The Neocomian series, such as was known to continental 

 geologists, could hardly be recognized in Britain ; and it was only during the last 

 portion of that period that any deposits took place in this country. The phenomena 

 of the "Wealden deposits might, he believed, be traced over a much larger area than 

 was commonly supposed, and certainly as far as Saxony. He considered that the 

 same area of land continued through both the Jurassic and the Cretaceous times. 



Prof Eamsay thought that the Purbeck strata were connected with lagoons in 

 contiguity with a large river rather than with inland lakes. These, from time to 

 time, owing to oscillations of level, were covered with marine deposits. He did 

 not think that the absence of gravelly deposits offered any serious difficulty in re- 

 garding the Wealden strata as marine. It seemed to him more probable, however, 

 that the sands and clays of the Wealden were due to some ancient rivers on a large 

 scale, and deposited at their mouths, though in some spots the beds were subject to 

 the action of fresh and salt water alternately. To the east of Oxford the Lower 

 Greensand beds were found at first to contain marine shells ; but as they proceeded 

 eastward freshwater forms made their appearance, and in places at last predominated 

 in beds of the same lithological character. He regarded the Neocomian as, to some 

 extent, a marine representative of the Wealden, though of later date. 



Mr. Etheridge recalled the fact that Mr. Judd had correlated the Punfield fossils 

 with those of the north of Spain, twenty- two species found in each being absolutely 

 identical. He argued from this that the extent of the beds may have been far larger 

 than might be supposed. In Hanover the beds, characterized by different Am- 

 monites, occurred in precisely the same order as in England at Speeton and else- 

 where. He regarded the question between Mr. Judd and the author of the paper as 

 not yet absolutely settled, though both had done so much for its elucidation. 



Prof. T. Rupert Jones remarked that the Purbeck-Wealden lake theory had not 

 only been intimated by several previous writers, but had been illustrated by maps by 

 Messrs. Godwin-Austen and Searles Wood, Jun. Whatever the direction of the 

 main rivers, and whatever the extent of the lakes, the Eev. Osmond Fisher had 

 shown that one river came in from the west. Mr. Jones instanced, in support of 

 the lake-theory, the occurrence of oysters, Potamides, and Corbulce in the base of the 

 Wealden at Pounceford; also the dwarf Tornatella Popei at Tunbridge WeUs 

 and Balcombe. He alluded also to the brecciated condition of some and the upturned 

 position of other Wealden beds. In allusion to the small bivalve Entomostraca so 

 often referred to, he regretted that they had not yet been fully described ; a bed of 

 them occurred in the Upper Portland at Hartwell before the Purbeck set in. He 

 concluded by saying that such general papers as the one under discussion ought to 

 have detailed references to the writings and opinions of previous observers. 



Mr. Hulke referred to the question of gravels being present in the Wealden, which 

 he stated were in some localities abundant, getting coarser in the beds furthest to the 

 west. This increase in the coarseness of the gravel was suggestive of a river running 

 from west to east. In the east of the Isle of Wight he had found remains of 

 Plesiosaurus, a marine form, much more commonly than fui'ther west, which sup- 

 ported the same view. He mentioned beds between Brixton and Calbourne, in the 

 Isle of Wight, which appeared to him strictly analogous to those in Worborrow Bay. 



Mr. Jenkins disputed the identity of origin of the Purbeck and AVealden beds, 

 hme being abundant in the former and comparatively absent in the other, and there being 



