XVI. 
THE ORIGIN AND CONSTITUTION OF CHALK AND FLINT, 
WITH SPECIAL REFERENCE TO THEIR FORAMINIFERA 
AND OTHER MINUTE ORGANISMS. 
Ey Professor T. Eupert Jones, E.R.S., E.G.S. 
A Lecture delivered at Watford , 20 th January , 1885. 
Contents.— Introduction. Range of the Chalk. Order of Succession of the 
Cretaceous Formations. Origin and extent of the Chalk as a marine deposit. 
Extraneous Materials in the Chalk. Post-Cretaceous changes. Organic Remains 
found in the Chalk. Vertehrata. Invertebrata : — Molluscs, Annulosa, 
Echinoderms. Polyzoa and Corals. Sponges. Foraminifera, etc. Coccoliths, etc. 
Flint. Conclusion. 
Introduction. —The pleasing task I have undertaken to-night is 
to talk about the Chalk, its origin and its constitution. It is a very 
large subject, and divides itself into two or three branches, each of 
which might be made a lecture of itself. On one branch, namely, 
the geographical range of the Chalk, you have had a very interest¬ 
ing lecture by my friend Mr. J. Logan Lobley a few years ago.* 
Another lecture, by Professor Morris, gave much valuable inform¬ 
ation about the Tertiary Eeds overlying the Chalk of the South-east 
of England. | 
Range of the Chalk. —Of course I shall not trench upon the 
ground traversed in the two Lectures to which I have alluded; 
and you must be so kind as to remember the chief geological 
facts and inferences as to the range of the Chalk,—namely, that 
it belongs to a very extensive set of strata reaching northward 
and eastward in England from the coast of Dorsetshire, with its 
outcrop at the surface across Wiltshire, Eerk shire, Eucks, and 
Herts, to Cambridge and away to Yorkshire; and showing itself on 
the south-east in the extensive but narrow tracts of the Hampshire 
hills and the North and South Downs. Of course you are aware 
that this does not show the whole of the Chalk. Looking at one of 
the diagrams on the wall, those of you who have not thought much 
of the matter will understand what we mean when we say that the 
Chalk crops out, is exposed, or forms the surface here and there; 
for, in this section, J reaching from Hampshire into the London area, 
you will see that there is an arching in the lines representing strata 
of Chalk and overlying Tertiaries, and the centre of the arch, comes 
up to the surface at Salisbury Plain and thereabout, exposing the 
Chalk ; but away to the south and to the north-east the same set of 
lines is covered up with those of other strata, such as the Thanet 
Sands, Woolwich-and-Eeading Eeds, and London Clay, which are 
found also in this neighbourhood or not very far off. Looking 
abroad, geologists find that the Chalk, that is, the upper portion 
of the Cretaceous series of strata, occurs not only in Great 
* ‘ Trans. Watford Nat. Hist. Soc.,’ Vol. I, Part 1, p. 1. 
t Ibid., Vol. I, Part 4, p. 89. 
+ Copied from Prof. Prestwick s paper, ‘ Quart. Journ. Geol. Soc.,’ vol. x, pi. i, 
fig. 1. 
VOL. III.—PART V. 
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