England and the " Red Chalk" of the Eastern Counties. 159 



The lower part of the Upper Gault, the rostratus-zone (or " inflatus- 

 zone ") of stratigraphical classifications, yields numerous fossils 

 that are not found in the Lower Gault. Species of ammonites that 

 have been referred to alike under the name A. varicosus here make 

 their aj^pearance, and these, as well as a number of peripherally 

 keeled shells, are readily distinguishable from any of the forms 

 occurring at lower horizons. Species of well-ribbed hoplitid 

 ammonites also occur. These bear considerable resemblance to 

 the hoplitids of the interruptus-Gault, and have proved a stumbling- 

 block for the unwary. When ill-preserved and crushed, they may 

 be difficult to distinguish from the comparable forms of earlier date ; 

 when well-preserved, the character of their peripheral area, as 

 pointed out to us by Dr. L. F. Spath, provides a good distinguishing 

 feature. Some descendants of these species show in their individual 

 development a rapid loss of the costate ornaments, so that the later 

 growth-stages are devoid of ribs and only retain remnants of th& 

 sculpture at the umbilical and peripheral margins. Such forms occar 

 in Price's Bed XI at Folkestone and in the sandstones below the 

 Chert Beds of the Upper Greensand in the Isle of Wight, as well as in 

 corresponding strata near Devizes. Specimens of them exhibited 

 in museum-collections have been variously and erroneously labelled 

 "Ammonites auritus", "A. splendens " , "A. catillus", and "A. 

 auritus, var. catillus ". Certain well-sculptured hoplitids found 

 rarely in the " Red Chalk " of Norfolk and Lincolnshire have been 

 ascribed to " Ammonites interruptus ". These are in reality species 

 of the Upper Gault and cannot be used in support of the contention 

 that the so-called Red Chalk represents the Lower Gault as well as 

 the Upper Gault. 



Other fossils which are of great stratigraphical value are 

 Inoceramus anglicus Woods and /. sulcatus Parkinson. The first 

 of these makes its earliest appearance at the base of the Upper 

 Gault and is abundant at some localities, as at Speetou. Inoceramus 

 sulcatus, recognizable even in a fragmentary state, is first met with 

 in Price's thin Bed VIII at Folkestone. It occurs also in Bed IX, 

 becoming large and abundant at the top of that bed, where it 

 suddenly dies out. Its vertical range is similarly limited in other 

 parts of the country. The reliance that can be placed on the evidence 

 of the above-named Inocerami when applied to stratigraphical 

 purposes rests upon abundant experience of their restricted range, 

 and is strengthened by evolutionary considerations. 



Although overlapping Gault has been described and mapped over 

 extensive areas in this country, no attempt has apparently been 

 made to ascertain whether this evidence of depression of the sea- 

 fioor points to one general movement or to several subsidences, 

 leaving separate local effects. It seems to have been accepted that 

 the Lower Gault is present at the unconformable junction in North 

 Dorset, Wiltshire, Oxfordshire, Buckinghamshire, and Bedfordshire, 

 where the mapping has established the general occurrence of a 



