Vol. 59.] A LOWEK-GKEENSAND FOSSILIEEROTJS BAND. 247 



Lower-Greensand facies, especially in the case of the pectens ; 

 hut the more thoroughly these fossils are studied, the more widely 

 are they found to range and the more doubtful does their value 

 in matters of correlation become. One of the Shenley x^ectens, 

 for example, is stated by Mr. H. Woods, our chief authority on 

 Cretaceous lamellibranchs, to present the distinguishing character- 

 istics of Pecten ductus, which has not hitherto been known to range 

 higher than the Tealby Limestone or the lower part of the ' zone 

 of Belemnites brunsvicensisJ But, as indicated in the list of fossils 

 (p. 263), other Shenley lamellibranchs are known to range both 

 above and below the horizon at which they are here found. 



So far as we have been able to discover, the nearest approach to 

 the Shenley fauna, more particularly as regards the brachiopods, 

 is found in the fossils from the Tourtia of Belgium; and in this 

 connection it is interesting to note that the Earingdon ' Sponge- 

 Gravels ' were at one time supposed to be of Upper-Greensand age, 

 chiefly on account of the kinship of some of their brachiopods with 

 those from the Tourtia. 1 Fortunately, one of us possesses a large 

 series of the Belgian fossils, which has enabled us to compare the 

 material in adequate quantity ; and this comparison has shown that, 

 while with some of the Shenley species there are minor differences 

 such as are generally observable in forms from widely separated 

 localities, the specific identity of many of the brachiopoda is un- 

 mistakable. These Tourtia-Beds (generally considered to be equiva- 

 lent to the Upper Greensand of England) lie at the base of the 

 Upper Cretaceous, where they mark a great unconformity, and appa- 

 rently always rest directly upon a floor of Palaeozoic rocks. Our 

 discovery of a closely- corresponding fauna below the English Gault, 

 by proving that many species supposed to be characteristic of the 

 Upper Greensand were in existence before the deposition of the 

 Gault, lends strong support to the more recent conclusions of 

 M. H. Parent, that the Tourtia in different localities includes deposits 

 ranging downward from the Albian into the upper part of the 

 Aptian. 2 



The reason for the apparently-anomalous relations of the Shenley 

 fauna is not far to seek. The deposits which represent the latest 

 stages of the Lower Cretaceous system in England are of great 

 irregularity, and only sparingly or sporadically fossiliferous ; so that 

 our knowledge of the life-history of the period after the deposition 

 of the Atherfield Clay is scanty and imperfect. The accidental 

 preservation of this fauna rich in brachiopods and other shells, at a 

 higher horizon in the Lower Greensand than had previously yielded 

 these fossils, has taught us that several species are of greater 

 antiquity than had been supposed. The greater depth and muddy 

 bottom of the Gault-sea were unfavourable to their continued 



1 T. Davidson, ' Monograph of the British Cretaceous Brachiopoda ' Pal. 

 Soc. vol. i( 1852) p. 3. 



2 Ann. Soc. Geol. Nord, vol. xxi (1893) p. 205 ; see also discussion by A. J. 

 Jukes-Browne in ' The Cretaceous Rocks of Britain ' vol. i, Mem. Geol. Surv 

 (1900) p. 383. 



