1872.] SOLLAS AND JUKES-BROWNE — INCLUDED KOCK-EEAGMENTS. "15 



fossils, for instance, which characterize the Gault of Folkestone. 

 The representative Cephalopoda seldom attain a large size ; of Gas- 

 teropoda and Lamellibranchs such genera as Rostellaria, Trochus, 

 Natica, Avicula, Spondylus, Area, and Pholadomya are certainly 

 dwarfed; while the small Plicatulce and Ostrece, which are known to 

 be truly Upper Greensand fossils, are very diminutive indeed. 

 Terebratula is fine and numerous ; Hhynchonella, Dentalium, and 

 Nucula, usually considered extra-tropical forms, are also numerous, 

 the two former especially so ; Echinoderms are rare, Crustacea not 

 very common, and both are small, as also the coral Smilotrochus and 

 the still more diminutive Micrabacea. 



In the Greensand of the Isle of Wight the fauna is very different : 

 Brachiopods are far less numerous, while Echinoderms and Cepha- 

 lopoda become finer ; Cardium, Cucullma, Gryphcea, Pectunculus, 

 Thetis, and Trigonia occur as new and seemingly more tropical 

 forms. The Gault unfortunately is thin and unfossiliferous in this 

 locality, so tbat we have not the opportunity of comparing the fossils 

 of its upper layers with those of the Cambridge Greensand ; but the 

 fine Ammonites and Hamites of the Folkestone Gault are well 

 known and bespeak a more favourable climate. 



Supplementary Notes. 



i. Since the reading of the above communication we have had 

 the good fortune to find a block of massive Labradorite about a 

 cubic foot in size and incrusted with coprolite ; this would seem to 

 be a Norwegian erratic. 



ii. Mr. Seeley states that he has found the well-known concre- 

 tions of the Magnesian Limestone in our formation ; and since 

 these concretionary forms are peculiar to the Magnesian Limestone of 

 IS". E. England, their occurrence strengthens our conclusions as to 

 the northern derivation of the Cambridge erratics, as does also 

 the occurrence of Poteriocrinus, likewise met with by Mr. Seeley. 



iii. Since the boring at Kentish Town passed through 14 feet of 

 Upper Greensand and 130 feet of Gault above Palaeozoic rocks, the 

 thicknesses being those of the southern area of the beds in question, 

 while at Hitchin there is only 1 foot of Greensand and over 200 of 

 Gault, and this Greensand is of the Cambridge coprolitic type, it is 

 probable that these two different types of Greensand were deposited 

 in different areas and separated by land now under the Hertford 

 Downs. In this way we would explain the evidence of cold con- 

 ditions in the Cambridge and Bedford area, while a comparatively 

 warm sea existed over Southern England. 



Discussion. 



Mr. Seeley gave some history of the specimens in the Wood- 

 wardian Museum, on which the paper was partly founded, some of 

 which had been collected by the late Mr. Lucas Barrett, and others 

 by himself. He thought that some of the scratches on one of the 

 specimens from Granchcstcr might be of modern origin, and doubted 



