Geological Age of the Sandringham Sands Geological Survey of Great Britain of Practical Geology, Form and Museum the Sandringham Sands, up to I 00 Ft

1100 NATURE June 17, 1961 voL. 190 waters of low salinity. Perhaps the lowered concen the excavated material. This means that any tration of the preferred calcium ions stimulates equivalent of the Suettisham Clay (Barremiau) of acceptance of less desirable ions for shell construction. north Norfolk or the Valanginian-Hauterivia.n On the other hand, sodium is probably interstitial, and sequence of Lincolnshire is either absent or is present thus reflects salinity directly. only in greatly attenuated form. As cha.ra.oteristic differences in tolerance for trace It is now clear that the Sandringham Sands are element concentrations a.re found among even closely wholly or in part of Berriasian age and that in the 1 related ta.xa •2, the responses of other pelecypods are West Dereham area the hiatus at their top is probably still conjectural. However, trace elements in fossil as great or greater than that at their base. It is not shells of Orassostrea virginica may be studied with the yet possible, however, to say precisely where this aim of establishing palreosalinities. Presumably, the fossil band in the Sandringham Sands fits in with accuracy of palreotemperature determinations by the the fragmentary Berriasian successions in Lincoln oxygen isotope method may be enhanced by pa.lreo shire and Yorkshire. In the Spilsby Sandstone there salinity corrections. are three distinct ammonite-levels, all characterized This research was supported in part by a grant by forms of Subcraspedites ; the lowest, with the from the Petroleum Research Fund administered by sub-genus Paracraspeditea, is thought to be more or the American Chemical Society, for which we are less contemporaneous with the basal Berriasian of grateful. East Greenland3• Subcraspeditea is found both JAMES B. RUCKER above and below Heetoroceras in East Greenland, so JAMES W. VALENTINE that the most likely position of the Norfolk Hectoro within or just above that Department of Geology, ceras fauna is a horizon of Missouri, of the Spilsby Sandstone. University a preliminary strati Columbia.. Dr. Larwood is preparing graphical account of the section. The Geological 'Turekian, K. K., and Armstrong, R. L., J. Mar. Ru., 18, 188 (1960). Survey material referred to above is being further • Valentine, J. W., Petrol. Ru. Fund, Third Rep. Res., 58 (1959). examined. R. CASEY Geological Age of the Sandringham Sands Geological Survey of Great Britain of Practical Geology, form and Museum THE Sandringham Sands, up to I 00 ft. thick, Exhibition Road, in the basal member of the Cretaceous System South Kensington, London, S.W.7. Norfolk and rest unconformably on the Jurassic in the Cretaceous 1 Spath, L. F., Mt-dd. om Grtmlanfossils A FRACTION of the total rainfall that reaches the indicative of a Berriasia.n (Infra-Valanginian) fauna ground water-table is called the effective rainfall1. new to Britain. Where there is irrigation, a fraction of the irrigation The fossils occur as clustered moulds in nodular water also has been found to contribute to the rise of masses of hard, grey-brown, glauconitic sandstone the water-table•. Effective values of rainfall and with carbonized plant debris, about 30 ft. above the irrigation are usually determined using lysimeters•. base of the formation. Twenty-eight genera of The lysimeters, however, need correction for their Mollusca have been identified, mostly lamellibranchs, size and the indications obtained from them are often Ast-arte (Neocrassina), Pholadomya, Panopea, Hart high. A general figure found at Amsterdam dune wellia, Iaocyprina, Thracia, Myophorella and Isodonta water works, where there was no run-off, indicated predominating. Cephalopods are represented by that 61 per cent of a total rainfall of 659 mm. per well-preserved examples of the ammonite Hectoro annum was effective1• An actual determination of the ceras, described by Spath1 in 1947 from S.W. Jameson rise in water-table over large areas has also been Land, East Greenland, and by numerous hollow carried out by means of open well water measure moulds of belemnite guards, including those of ments•••. The effective values of rainfall and irriga AcroteuthiB. Some of the lamellibranch and belemnite tion, however, do not seem to have been arrived at. species occur also in the Spilsby Sandstone (Berria An analysis of the changes in the ground-water level sian) and superjacent Neocomian strata. in Lincoln has therefore been taken up in this investigation, and shire ; others, such as the species of Hartwellia, the effective values of rainfall and irrigation were Isocyprina and Isodonta, have their closest parallels evaluated from the (fortnightly) measurements of the in the Upper Jurassic (there is no previous record of water-levels recorded for the past 20 yr. in thirteen Isodonta in the British Cretaceous, for example). wells randomly distributed over 565 acres of irrigated Many of the shells were ravaged by the boring fa.rm area of the Indian Agricultural Research polyzoan (kaysonia, only recognized recently in the Institute, New Delhi. 1 Cretaceous fe~as of Britain•. Fig. I gives the mean water-table levels on July The fossiliferous sandstone is followed within a few of each year, from 1940 to 1950, just before the begin feet by the Lower Greensa.nd (Aptian-Lower Albian), ning of the monsoons. This period is selected to be this determination being suggested by a rolled suitable as the water would reach a stable level just specimen of the ammonite Deahayesitea found ameng before the monsoons start8• The trends in the rise of