CORRESPONDEKCE. 
55 
crossing this line, 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 
Greensand 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 Mhyncho- 
nella depressa, R. latissima, R. nuciformis, Terehratula Nerviensis, T. oh- 
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, tliat, for the sake of 
argument, I will suppose tlie fact to be admitted. In which case, the 
lowest beds of the Greensand in Dorset and Dpvonshire 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 whicli 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 Fitton 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 J[f/c;/?a RauUniana, Exo- 
gym undata, and E. undulata ; from Slianklin, Astarte furmosa, Cardlum 
Hillanum, Fsammohia stnatula, Tellina incpqnaUs, GevvilUa lanceolata, 
Thetis minor, T.lcevigata, Venus faha, TA ma semi sulcata, Nucula impressa, 
N. lineata, Pecten quinquecoslatus. Pinna ietragona, Corhula elegans, 
Tngonia caudata, Litlorina conica, L. monilifcra, and L. roiundata. 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 de|X)sits. 
_ In the accompanying map I have endeavoured to show the probable posi- 
tion of land and water at two distinct periods: the 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 Fitton'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 as above stated, 
the abundance of the Blackdown fossils, as compared with those in the 
upper division of the Greensand in Surrey, etc., would not be at all sur- 
