GAULT. 383 



UPPER CRETACEOUS. 

 The Upper Cretaceous strata are divided as follows : — 



3. Chalk. 



2. Upper Greensand. 



I. Gault. 



These strata are intimately connected, for it is frequently difficult 

 to fix any divisional line between the Chalk and Upper Greensand, 

 and between the Gault and Upper Greensand.^ In Devonshire the 

 Blackdown Beds probably represent littoral deposits of the age 

 of the Gault, as well as Upper Greensand. 



GAULT. 



The term Gault (spelt also Gait or Golt) is a local name in Cam- 

 bridgeshire for unctuous clay, and from its application in that 

 district to the strata now under consideration, the term came to be 

 restricted to them; it was used as early as 1788 by the Rev. John 

 Michell. The term Blue Marl was used by William Smith (1812): 

 and the name Albian given by D'Orbigny (from the department of 

 the Aube) is sometimes applied. 



The Gault may be described as a stiff blue or pale bluish-grey 

 clay, sometimes calcareous or sandy and micaceous, and now and 

 then containing indurated nodules and small septaria. Nodules 

 and crystals of iron-pyrites are abundant, and many of the fossils 

 are pyritic : small crystals of selenite are not uncommon. A layer 

 of iron-grit occurs at its base in parts of Sussex ; but in this 

 position there is generally found a band of phosphatic nodules. 



The thickness of the Gault is at Folkestone 100 feet, at Maidstone 150 feet, and 

 in the boring at Chatham, 193 feet. At Caterham, a thickness of 343 feet was 

 proved in a well. In Wiltshire it varies from 70 to lOO feet ; in Oxfordshire and 

 Berkshire it is about 250 feet ; and in Buckinghamshire upwards of 200 feet. 

 Near Cambridge it varies from 115 to iSo feet, and between Arlesey and Ashwell, 

 and at Hitchin, from 180 to over 200 feet. Near Downham Market it may be about 

 60 feet ; it was proved in a well sunk at Holkham, near Wells, in Norfolk, 

 10 "feet; and at Norwich (Carrow Well), about 38 feet. In deep borings at 

 Harwich it was 61 feet thick, and at Kentish Town, London, 130 feet. 



The Gault at Folkestone (Folkestone ]\Iarl) has always been a 

 famous collecting-ground for fossils ; since the formation may be well 

 studied at Copt Point, and its brilliantly-coloured fossils may be 

 seen exposed at low tide on the fore-shore of East Wear Bay. The 

 organic remains, being mostly pyritic, are liable to rapid decay, and 

 although abundant, it requires care and patience to collect a good 



1 W. Whitaker, P. Geol. Assoc, v. 497 ; Godwin-Austen, Q. J. vi. 461 ; Judd, 

 Q. J. xxvii. 222; J. S. Gardner, Q. J. xl. 122; A. J. Jukes-Browne, G. Mag. 

 1877, P- 363. 



