A HISTORY OF RUTLAND THE UPPER LIAS This division occupies a considerable area in the western half of the county, though its surface is largely concealed by the Pleistocene deposits. It consists entirely of clays, which form the steep slopes be- neath the escarpments of the Inferior Oolite : this mass of clay has a thickness of from i6o to i8o feet and is divisible into two zones, a lower zone oi Ammonites serpentinus, which is only a few feet thick, and an upper zone of A. communis, which includes the rest of the division. Between the Middle and Upper Lias there are usually a few inches of red or yellow sandy clay which is known as the ' Transition bed ' and yields a mixture of fossils belonging to the two divisions. Above it are the ' Paper Shales,' 12 to 18 inches of bluish-grey shale including one or more lenticular layers of argillaceous limestone ; these beds yield remains of fish and insects chiefly in the form of scales and fragments. The fish belong to the genera Lepidotus, Lepto/epis and Pachycormus, but complete specimens are rare. The shales are succeeded by a grey marly clay and a layer of hard ferruginous limestone in which Ammonites are abundant, the commonest being the species known as A. serpentinus, A. exaratus, A. communis and A. Holandrei. The zone of A. communis has at the base a few feet of bluish marly clay, at the top of which are some thin layers of limestone con- taining an abundance of the characteristic Ammonite. Above this band come about 60 feet of dark blue clays without fossils. Then comes another fossiliferous band distinguished by the abundance of small spiral univalve shells, especially Cerithium armatum, and by the prevalence of Ammonites Jibulatus and Nucula Hammeri. These have been termed the Lower Leda Beds or Cerithium Beds by Mr. Beeby Thompson.^ Clays without fossils succeed and are surmounted by others in which fossils occur ; the latter are the Upper Leda Beds which may possibly belong to a higher zone than that of A. communis, since Mr. Thompson has pointed out that they contain some fossils which are characteristic of the zone of A. jurensis in Yorkshire. The Upper Lias clays furnish good material for the manufacture of bricks, tiles and drain-pipes. THE NORTHAMPTON SANDS There is evidence that the Upper Lias had undergone a certain amount of erosion before the deposition of the Northampton Sands, for the base of the latter often contains pebbles of argillaceous stone which have evidently been derived from the Lias, and are covered with Serpulce or bored by lithodomus molluscs. This break in the succession is not however one of great magnitude, on the contrary it can only be a part of the zone of A. jurensis, which is missing, for that ammonite is found in the Northampton Sands.
- In papers on the Liaj of Northamptonshire in the Journal rf the North Nat. Hist. Soe. vols, iii, iv,
and V. (1884-8). 4
