322 JURASSIC. 



MIDDLE OOLITIC. 



OXFORD CLAY. 



The Oxford Clay consists of dark-blue, purplish, yellowish, and 

 slate-coloured clay and shale. Calcareous and bituminous varieties 

 are met with here and there. It contains much iron-pyrites and 

 selenite, and many septaria. The name is derived from the county 

 in which it is well developed ; originally it was termed the ' Clunch 

 Clay and Shale,' by William Smith. ^ The name Oxford Clay was 

 used by Conybeare in 1822. Near its base there occur in places 

 beds of sand and calcareous sandstone, sometimes of a concretionary 

 nature and very fossiliferous, termed the Kellaways (or Kelloway) 

 Stone or Rock, by W. Smith, in 18 15, from Kellaways, north-east of 

 Chippenham, in Wiltshire. 



The thickness of the Clay varies from 300 to 600 feet ; and that 

 of the Kellaways Rock from 5 to 80 feet, and upwards. The term 

 Oxfordian, proposed by D'Orbigny, is sometimes used for the strata. 

 Some authorities are disposed to rank the Kellaways Rock as a 

 distinct division, termed the Callovian by D'Orbigny in 1852. 

 This may be useful on the Continent, but in this country the 

 Kellaways Rock must be regarded as the irregular basement-bed of 

 the Oxford Clay ; for it is not a persistent bed, and the sandy 

 sediments run up irregularly into the Oxford Clay. 



The beds are sometimes (palKontologically) divided as follows : — 



3. Beds with Ammonites belonging to the ' Cordatiis' group {A. cordafus, A. 



Lanibcrli, etc.). 

 2. ,, ,, Ammonites belonging to the '' OniaUts'' group {^A. Jason, A. 



oniatns, A. athlcta, etc.). 

 I. ,, ,, A7nino)utcs CaUoz'iciisis,A.i)iacrocepJiah(s,AncylocerasCalloz<ieiise. 



(Kellaways Rock). 



The fossils of the Oxford Clay include the Coral Anahacia 

 orhuUtes ; the Annelide Scrpida vcriehralis ; and the Echinoderms, 

 Extracrimis and Acrosalenia sphiosa, etc. ; but as with other clay 

 formations like the Lias and the Kimeridge Clay, there are few 

 Urchins. Among other fossils, there are Avicida mccqiiivalvisy 

 Gryphaa dilaiata abundant, Ostrea Marshii {flabelloides), Pecten 

 fibrosits, CiiciiUcEa concintia, Modiola bipariita, M. cuneata, NucuJa 

 7iuda, Thfacia dcpressa, Trigonia clavellafa, T. elongala, T. irregularis ; 

 Waldheimia {Te7'ebratula) imp7'essa, Rhynchonella varians, Discina 

 latissima ; Ammonites excavaiiis, A. vcrlebralis, A. Bakeries, A. MaricF., 

 A. Goioerianiis, A. Jason^ and other species previously noted ; 

 Nautilus hexagonus, Belemnites hastaius, and B. Oivenii {puzosiattus) 

 which attains large dimensions. 



Fossil coniferous wood has been found, also leaves of Zamia. 

 Remains of the Reptiles Ichthyosaurus, Ophthalmosaurus, Plesio- 



^ Clunch is a provincial term for any coarse clay. 



* A. Diiiicani, A. Gulielmi, and A. Elizabet/uc have been regarded as varieties 

 oi A, jfasoii. 



