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GAULT

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Originally appearing in Volume V11, Page 534 of the 1911 Encyclopedia Britannica.
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GAULT , in See also:

geology, one of the members of the See also:Lower Cretaceous See also:System. The name is still employed provincially in parts of See also:England for a stiff See also:blue See also:clay of any See also:kind; by the earlier writers it was sometimes spelt " See also:Galt " or " Golt." The formation now known as Gault in England has been variously designated " Blue See also:Marie," " See also:Brick See also:Earth," " Golt Brick Earth " and " See also:Oak-See also:tree-See also:soil." In certain parts of the See also:south of England the Gault appears as a well-marked See also:deposit of clay, lying between two sandy formations; the one above came to be known as the " Upper See also:Greensand," the one below being the " Lower Greensand " (see GREENSAND). Since the typical clayey Gault is continually taking on a sandy facies as it is traced both horizontally and vertically; and since the fossils of the Upper Greensand and Gault are inseparably related, it has been proposed by A. J. See also:Jukes-See also:Browne that these two See also:series of beds should be regarded as the arenaceous and argillaceous phases of a single formation, to which he has given the name " Selbornian " (from the See also:village of See also:Selborne where the beds are well See also:developed). Lithologically, then, the Selbornian includes the blue and See also:grey See also:clays and marls of the Gault proper; the glauconitic sands of the Upper Greensand, and their See also:local See also:equivalent, the " maim," " maim See also:rock " or " firestone," which in places passes into the micaceous See also:sandstone containing sponge spicules and globules of See also:silica, the counterpart of the rock called " gaize " on the same See also:horizon in See also:northern See also:France. In See also:Yorkshire, See also:Lincolnshire and parts of See also:Norfolk the Selbornian is represented by the Red See also:Chalk. The maim is a ferruginous siliceous rock, the silica being mainly in the colloidal See also:condition in the See also:form of globules and sponge spicules; some See also:quartz grains, See also:mica and See also:glauconite are usually See also:present along with from 2 to 25% of calcareous See also:matter. Chert-bands and nodules are See also:common in the Upper Greensand of certain districts; and calcareous concretions, locally recognized as cowstones (Lyme Regis), doggers or buhrstones, are not infrequent. The See also:principal divisions of the Selbornian See also:stage with their characteristic zonal fossils are as follows: See also:Warminster Beds Pecten as per and Cardiaster fossarius. Upper Gault See also:Devizes Beds or Merstham Beds with Schloenbachia rostratus. Hoplites lautus.

Lower Gault H. interruptus. Acanthoceras mammillatum. The Gault (with Upper Greensand) crops out all See also:

round the See also:Wealden See also:area; it extends beneath the See also:London See also:basin and reappears from beneath the northern scarp of the Chalk along the See also:foot of the Chiltern Hills to near See also:Tring. In the south of England the Gault clay is fairly See also:constant in the lower See also:part, with the Greensand above; the clay, however, passes into See also:sand as it is followed westward and, as already pointed out, the clay and sand appear to pass into a red chalk towards the See also:north-See also:east. The Gault overlaps the Lower See also:Green-sand towards the east, where it rests upon the old Paleozoic See also:axis; it also overlaps the same formation towards the See also:west about See also:Frome, and thence passes unconformably across the See also:Portlandian beds, Kimeridge Clay, See also:Corallian beds and See also:Oxford Clay; in south See also:Dorsetshire it rests upon the Wealden Series. The Gault (with Upper Greensand) passes on to the See also:Jurassic and See also:Rhaetic rocks near Axmouth, and oversteps-farther westward, in the Haldon Hills, on to the See also:Permian. A large outlier occurs on the Blackdown Hills of See also:Devonshire. See also:Good localities for fossils are Folkestone—where many of the shells are preserved with their See also:original pearly nacre,—Burnham, Merstham, Isle of See also:Wight, the Blackdown and Haldon 'Hills, Warminster, See also:Hunstanton and Speeton, See also:Black See also:Venn near Lyme Regis, and Devizes (malmstone and gaize). The beds are well developed in the vale of Wardour, and in the Isle of Wight; the Gault forms the so-called " blue slipper " at See also:Ventnor which has been the cause of the landslip or undercliff. The Gault of north France is very similar to that in the south of England, but the See also:French See also:term Albien includes only a portion of the Selbornian formation. The Gault of north-west See also:Germany embraces beds that would be classed as Albien and Aptien by French authors; it comprises the " Flammenmergel "—a See also:pale siliceous See also:marl shot with See also:flame-shaped darker patches—a clay with Belemnites minimus, and the Gargasmergel " (See also:Aptian). In the Diester and Teutoberger Wald, and in the region of See also:Halberstadt, the clays,and marls are replaced by sandstones, the so-called Gault-Quader.

See also:

Continental writers usually See also:place the Gault or See also:Albian at the See also:summit of the Lower Cretaceous; while with See also:English geologists the practice is to commence the Upper Cretaceous with this formation. In addition to the fossils already noticed, the following may be mentioned: Acanthoceras Desmoceras Beaudanti, Hoplites splendens, Hamites, Scaphites, Turrilites, Aporrhais retusa, Trigonia aliforme, also See also:Ichthyosaurus and Ornithocheirus (Pterodactyl). From the clays,. bricks and tiles are made at Burham, Barnwell, See also:Dunton Green, Arlesey, See also:Hitchin, &c. The cherts in the Greensand portion are used for road See also:metal, and in the Blackdown Hills, for See also:scythe stones; hearthstone is obtained about Merstham; phosphatic nodules occur at several horizons. See CRETACEOUS SYSTEM; ALBIAN; APTIAN; also A. J. Jukes-Browne, " The Gault and Upper Greensand of England," vol. i., Cretaceous Rocks of See also:Britain; Mem. Geol. Survey, 1900.

End of Article: GAULT

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