TRANSACTIONS OP SECTION C. 393 



The block is fairly angular, approximately a cube. On one side the fracture 

 of the bed is fairly fresh ; the opposite side is slightly hollowed, as if by the 

 long-continued current action of a shingly stream. For the greater part of its 

 thickness it is a true sarsen ; towards the base a few flint pebbles are scattered 

 through it; the upper surface passes into a true ' puddingstone ' (an agglutinated 

 mass of flint pebbles), the matrix of which is lithologically the same as, and 

 continuous with, the material of the sarsen. About the middle of the upper 

 side the agglutinated mass of pebbles fills a small gully in the quondam sand of 

 the sarsen (three photographs shown). A subordinate alternation of the true 

 sarsen structure with the pebble-bed structure is seen in the largest examples 

 of puddingstone perhaps in the county. 1 A striking lithological feature of 

 this specimen is the distribution in it of numerous small angular bleached frag- 

 ments of flint. Its dimensions are 30 inches X 20 inches X 18 inches, and its 

 weight not less than half a ton. No trace of glacial striations has been detected 

 on it. 



The author refers to his former work on the genesis and distribution of the 

 sarsens. 3 While recognising their common occurrence in the Lower Eocenes, 

 and even in the sands of the Neocomian, he regards those of the interior of the 

 London Basin as the wreckage of a younger formation (late Eocene or Oligocene), 

 possibly the stratigraphical freshwater equivalents of the Stettiner Sandstein of 

 North Germany 3 and the Gres de F ontainehleau i of the Paris Basin. Agglu- 

 tinated portions of the Bagshot Pebble Beds in situ, with similar siliceous 

 cementation, are known to occur ; 5 there is good evidence of the quondam exten- 

 sion of the younger beds of the Bagshot Series (including the pebble beds) over 

 Herts and Essex ; and the author points to this recently unearthed rock-mass 

 as tending to clinch the view advocated by him for years past — that the sarsens 

 and the Herts ' puddingstone ' are remnants of one and the same younger 

 Eocene (or Oligocene) formation. 6 He considers the latest treatment of the 

 subject by the late Professor T. Rupert Jones, F.R.S., and the more recent 

 treatment of it by H. B. Woodward, F.R.S., 7 inadequate. 



6. Wealden Ostracoda. By F. Ross Thomson. 



This paper was intended to describe and illustrate the Ostracoda of the 

 Wealden formation, as they have never before been thoroughly investigated. 



Those of the Purbeck formation have been worked out by the late Professor 

 Rupert Jones, and in his paper on the subject, published in the ' Quarterly 

 Journal of the Geological Society,' he stated that he hoped to be able to treat in 

 full the Wealden Ostracoda at a future opportunity, but his intention was 

 unfortunately never carried out. 



He gave a list of the fossils common to the Purbeck and Walden so far as 

 he wae able to do so at the time he wrote, viz., in 1885, but his list as regards 

 the Wealden appears to be inaccurate and incomplete, and the object of this 

 paper was to classify and bring up to date what he had left undone. 



It was pointed out that the principal Wealden form, Cyprus Valdensis, is 

 triangular and bean-shaped, and does not possess the antero-ventral notch so 

 common to other forms, but Fitton, Rupert Jones, and the German geologists, 

 Dunker and Roemer, seem to have mistaken Cypridea punctata for this fossil. 



A full list and detailed description of those forms that have now been found 

 to belong to the Wealden formation were given, and photographs of them in 

 the matrix were shown. 



1 Seen in the grounds of Oak Hall, Bishop's Stortford (G. E. Pritchett, Esq., F.S.A., 

 who has furnished photographs). 



2 P. G. A., viii., No. 3 (1883), where critical reference is made to the views of 

 the late Professor John Phillips, F.R.S. , of Oxford. 



fl H. Credner : G&ologie (Leipzig), 10th ed., pp. 692 ff. 



4 S. Meunier : Les causes actuelles en Giologie (p. 289) ; Credner (op. cit.), p. 683. 



1 A. Irving : P. G. A., xv. (February 1898), pp. 196, 236. 



6 A. Irving : « High Level Plateau Gravels, &c.,' Geol. Mag., No. 484, October 1904. 



7 ' The Geology of the London District,' Mem. Geol. Surv., 1909. 



