2
one of which a hundred specimens may be easily obtained in a few
minutes, is obviously misleading.....it is the abundant rather
than the rare species which are important, and shells which are seldom
found in collections, as it is difficult to obtain them whole, are some-
times among the most characteristic of the deposit in which they
occur."1
It will be found, however, that very few of the species in the
published lists of the Crag fossils are unrepresented in the
Museum Collection, and though imperfect specimens are
admitted for want of better, such will be few and far between.
We would earnestly recommend the study of fragments, and the
determination, as far as is possible, of at least the genus of the
shell-fragments composing the bulk of the Crag. Thus trained,
the student could record approximately the species occurring in
a new exposure, although no single specimen was perfect enough
to be worth keeping, or all were too much decomposed to bear
removal from their natural positions ; such lists may prove of
far greater value than "cabinet specimens" from well-known
localities. The chief educational use, indeed, of any collection
lies in training students in the identification of other specimens,
and in the power to detect forms hitherto unrecorded. Probably
many such have been lost to science, simply because they were
not recognised in the field as unknown species, and were too
imperfect to be considered worth taking.
As one of the objects of the collection is the exhibition of
the whole assemblage of organisms co-existing at the time of
deposit, and as the scanty exposures in Essex have not furnished
good specimens in the case of many species, the richer deposits
of Suffolk and Norfolk have contributed the bulk of the series
exhibited.
I.—THE CORALLINE CRAG.
The lower of the two divisions mentioned above is dis-
tinguished by the name of the Coralline Crag, from its
abundant and beautiful Corallines (not true corals, as at first
supposed). It is a bed, about 80ft. thick, of clean shell-sand,
often passing into a soft limestone, largely consisting of the said
corallines. It was evidently formed in clear, but not very deep
water, and its most abundant shells indicate a somewhat warmer
climate than the present, although occasional Arctic forms show
that the sea was partially open to the north.
I Quart. Journ. Geol. Soc, vol. liv., p. 309. (1898.)