144 
PROF. T. RUPERT JONES—ORIGIN AND 
Britain, but in Denmark, North and South Bussia, Belgium, and 
Prance, with its equivalents in Bhenish Prussia, Westphalia, and 
elsewhere in Europe, and in North Africa and Western Asia, for an 
extent of nearly 3000 miles W. and E., by 1000 miles N. and S. 
Order of Succession of the Cretaceous Formations. —On the wall there 
is another section, to show a local outcrop of not only the Chalk, 
but of other beds which belong to the same geological system, and 
which preceded it in its formation. Thus the “ Chalk-marl,” the 
“Upper Greensand,” the “Gault,”and the “Lower Greensand” (the 
Uppermost Neocomian) are seen to succeed one another in the high 
Chalk escarpment passing through Berks, Bucks, and Herts. In 
some parts of the South-east of England the fresh-water Wealden 
Beds are the lowest of the Neocomian beds, and the so-called “ Lower 
Greensand,” which is a marine and upper member of the ssfme great 
formation (more developed on the Continent), succeeds with some 
clay beds, but with much thicker irony sands and sandstones. These 
are the Woburn Sands of Bedfordshire, etc., forming a wide sandy 
country below the Chalk escarpment, and divided from it by the 
hollow and often wet clay ground of the Gault. This last is about 
100 feet thick ; and northwards it passes into the “ Bed Chalk ” of 
Hunstanton. It is succeeded in Berks by 20 or 30 feet of “ Upper 
Greensand,” a soft calcareous sandstone with green (glauconitic) 
grains, which becomes thinner to the N.E., and gives place to the 
“Chalk-marl” or “Grey Chalk.” This is a tough argillaceous 
chalk, at some places greenish and sandy; and near Cambridge its 
base consists of a thin bed of rolled nodules and broken fossils 
(derived from the Gault), sufficiently phosphatic to be worked for 
the manufacture of manures. Elsewhere, as in Bucks, for instance, 
the Chalk-marl is 80 feet thick, with some stony beds in it; on it 
there is the “ Totternhoe Stone,” two layers of hard, brownish- 
grey, sandy chalk, used for building, and about 6 feet thick ; then 
White Chalk (without flints), or “ Lower Chalk,” nearly 500 feet 
thick ; next comes another well-marked, thin, hard stratum, first 
recognised and called “ Chalk-rock ” by Mr. W. Whitaker.* 1 It 
is only about 4 feet thick, but has been traced for long distances, 
on account of its being a yellowish or cream-coloured chalk dividing 
up into green-coated nodular masses. It is rich in fossils, such as 
belong generally to the Lower Chalk; some small JBaculites and 
Scaphites are peculiar to this bed, and these I have met with in 
Kent in probably the same stratum. White Chalk (with flints), or 
“ Upper Chalk,” forms the upper portion of this Cretaceous Series, 
with a thickness of 300 feet. Thus the whole is about 890 feet 
thick in Buckinghamshire ; but it has a greater thickness in the 
Isle of Wight (1336 feet) and elsewhere.f 
* ‘Quart. Journ. Geol. Soc.,’ vol. xvii, p. 167 ; and ‘Mem. Geol. Surv., 
Explan. Sheet 7,’ 1864, p. 5. 
f See Horace Woodward’s ‘Geology of England and Wales,’ 1876, p. 250, 
etc. ; and Dowker, ‘ Geol. Mag.,’ vol. vii, p. 470. The student should also 
refer to Jukes-Browne on the Divisions of the Chalk, ‘ Geol. Mag.’ dec. 2, vol. 
vii, p. 248 ; and to C. Barrois’ papers on the Chalk, especially his ‘ Becherches 
sur le terrain cretace superieur de l’Angleterre et de ITrlande,’ 1876. 
