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By A. J. Jukes-Browne, B.A., F.G.S. 331 
marly portion of the Gault. Everyone who has described the 
Folkestone Gault has divided it into two portions, characterised by 
different species of Ammonites; now of the five Ammonites which 
occur in the Devizes Sandstone two (dm. rostratus and Am.» 
varicosus) are specially characteristic of the Upper Gault, two range 
throughout the Gault, and one occurs only in the Lower Gault at 
Folkestone, though elsewhere it is also found in the Upper. 
Again, if the Malmstone and Sandstone of Devizes formed a 
separate zone later than the Upper Gault, this Upper Gault should 
occur beneath the Malmstone; but we have seen that the fossils 
found in the old brickyard at Dunkirk were Lower Gault species. 
It is clear, therefore, that the sandstones which contain the Devizes 
fauna are merely a sandy facies of the upper portion of the Gault, 
or conversely that the Upper Gault of Folkestone is the argillaceous 
representative of what is elsewhere called Upper Greensand. 
It follows from this that the Gault and Greensand are uot distinct 
subdivisions, as generally supposed, but that the mass of the Green- 
sand was formed contemporaneously with the upper part of the 
Gault, and is sandy because it was formed nearer the shore of the 
western Cretaceous land. It is, indeed, very probable that at Black- 
down, in Devonshire, the whole of the Gault is represented in what 
is there called Upper Greensand; for the Blackdown fossils are 
almost identical with those of Devizes, and at the base there is 
some dark argillaceous sand. 
So long ago as 1850 Mr. Godwin-Austen was fully aware not 
only of the distinctness of the Lower Greensand for which he 
endeavoured to introduce the name Neocomian, but also of the fact 
that the Gault and Upper Greensand are merely different facies of 
one formation. Thus he writes (Quart. Journ. Geol. Soc., vol. 6, 
p- 461) :—“ In applying the names of Gault and Upper Greensand 
to the beds which underlie the Chalk along the line here described 
it is not intended to convey the notion that any separation can be 
traced between two well-defined groups, or that even any true sandy 
beds occur. Indeed there is no name in the whole series of geological 
formations so purely conventional as that of Upper Greensand.” 
Again, on p. 472:—“ The Gault, moreover, is not an independent 
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