COJtltliSrONDENCE. 



55 



crossing this lino, would act upon the edges of these various deposits, and 

 thus mingle in one stratum the debris of many. It would, further, serve 

 to connect the " pebble-beds " of Surrey with similar deposits in the Lower 

 Grccnsand near Devizes, and also with such part (at least) of the Faring- 

 don gravels as are generally recognized as of Lower Greensand age. The 

 mineral character is the same in each, and the fossils are also found to bear 

 a close resemblance. The " pebble-beds " of Godalming contain RhyncJw- 

 nella depress a, R. latissima, R. nuciformis, Terebratula Nerviensis, T. ob- 

 longa, T.faba, T. ovata, (?)T. tamarindus— the first four rarely, the latter in 

 abundance ; all of which species have been found at Seend, near Devizes, 

 and also at Farringdon. 



To the first part of this argument — viz. a northern, or rather north- 

 eastern, extension of the Greensand at this period, no objection is likely to 

 be made. A western extension at the same period, however, does not so 

 readily admit of proof ; yet it is so very probable, that, for the sake of 

 argument, I will suppose the fact to be admitted. -In which case, the 

 low est beds of the Greensand in Dorset and Devonshire would be nearly 

 equivalent in age to the "pebble-beds " of Godalming ; and the position 

 of the " Whetstone " beds of Blackdown, from which the greater portion of 

 the Blackdown fossils are obtained, would correspond with the concretionary, 

 siliceous, and calcareous deposits which so frequently occur near the base 

 of the ferruginous division of the Lower Greensand of Kent and Surrey, 

 etc. As, for instance, the concretions in the cliffs between Folkestone 

 and Copt Point, described by Fifcton as " in part consisting of siliceous, 

 spongy stone, like the Whetstone of Devonshire ;" the Bargate stone of 

 Godalming, in which siliceous, spongy concretions also occur ; the siliceous 

 and ferruginous concretions in the cliff, which form the upper part of 

 Shanklin chine, and the ferruginous nodules in the Greensand at Parham 

 Park. The fossils from these localities, though few in number, are mostly 

 Such as occur at Blackdown. Thus, from the Bargate stone of Godalming, 

 in which shells are very scarce, T have obtained Avicula Rauliniana, Jlxo- 

 gyra undata, and JE. wndulata ; from Shanklin, Astarte formosa, Cardium 

 Billanum t Psammobia striatula, Tellina incequaUs, GcrvilUa lanceolata, 

 Thetiti hi nio)', 7 T . hpvif/ala, f'entts /'aba, Lima semisnlcata, Xncula impressa, 

 N. lineata, Perfen f/nintjuccostafus, Pinna tetragona, Corbula elegans, 

 Trigonia caudata, Littorina conica, L. monilifera, and L. rotundata. In 

 fact, these last-named deposits contain a greater percentage of Blackdown 

 fossils than occur in any other portion of the Cretaceous series ; and this, 

 alone, is in itself the strongest argument which could be used in favour of 

 the Lower Greensand age of the Whetstone deposits. 



In the accompanying map I have endeavoured to show the probable posi- 

 tion of land and water at two distinct periods: t he darker shading represents 

 the probable extent of the greensand ocean over our south-eastern counties 

 during the accumulation of those deposits which are included in Fit ton's 

 middle and lower division ; the lighter shading exhibits its further exten- 

 sion to the north-east and west, during and after the accumulation of the 

 "pebble-beds," and previously to the deposition of the Gault. 



In this map Mr. Godwin-Austen's "old ridge" forms the northern boun- 

 dary of the Greensand during the first period. At the second period the 

 greensand is seen on the north— the ridge being partially submerged. It 

 is probable that this ridge became wholly submerged during or imme- 

 diately before the deposition of the Gault. 



Allowing the position of the land-surface to have been ;is above stated, 

 the abundance of the Blackdown fossils, ;is compared with those in the 

 Upper division of the Greensand in Surrey, etc.. w ould not be at all sur- 



