The Upper Jurassic Clays of Lincolnshire

Abstract

The broad tract of low country which extends from the Humber through the middle portion of Lincolnshire, and spreads out into the fen-country to the south, is underlain by a thick deposit of clay which, in the adjoining county of Cambridgeshire, has been called the “Great Fen-Clay“ * . The lower portion of this great pelolithic formation is undoubtedly of Oxford-Clay age, whilst its upper portion certainly belongs to the Kimeridge Clay. Owing to the absence of beds lithologically resembling those of the Corallian rocks of Yorkshire and the southern and south midland counties of England, no division corresponding in age to the Corallian has as yet been made out in Lincolnshire. Prof. Blake states that the Kimeridge and Oxford Clays here form one continuous formation †. In the Survey Memoir on this district it is mentioned ‡ that the Corallian group is entirely absent, and only the Oxford and Kimeridge Clays are mapped. Jukes-Browne goes still further, and states that “in Lincolnshire there is nothing to represent the Corallian group, the Oxford Clay merging gradually into the Kimeridge Clay“§. H. B. Woodward mentions that in Lincolnshire, Buckinghamshire, Norfolk, and probably Sussex, “the Kimmeridge and Oxford Clays come in direct sequence,“ and he adds that“ unless we imagine an unconformity— and there is no reason for this supposition—the Coral Rag and Calcareous Grit developed in Oxfordshire, Wiltshire, and Dorsetshire, are represented by portions of the Oxford and Kimmeridge Clays in the districts just mentioned“║. No attempt, however, has as yet been made to separate off a portion which would be equivalent to the Corallian of other areas. 3. Kimeridge Clay :— ( b ) Upper Kimeridge: thin papery shales, with Discina latissima . ( a ) Lower Kimeridge: dark clays, with septarian nodules, subdivided into:— (iii.) Clays with Amm. mutabilis, Astarte supracorallina , &c. (ii.) Clays with Amm. alternans . (i.) Clays crowded with Ostrea deltoidea . 2. Corallian . Black selenitiferous clays, with Amm. plicatilis, Amm. cawtonensis, Bel. abbreviatus, Gryphæa dilatata, Ostrea deltoidea , &c. 1. Oxford Clay , subdivided into five palæontological zones, with the Kellaways Rock at its base.