Geoscience Reference
In-Depth Information
decline and eventual disappearance of the southern forms of molluscs of the earlier
zones with the shells of northern species becoming steadily more and more
important.
3.3.2 The Red Crag
Succeeding the Coralline Crag in the geological table, the Red Crag, comprising
quartz-rich sandstone stained orange-red with iron oxides, lies unconformably
above the Eocene London Clay and was deposited a short distance offshore in a
warm and relatively shallow sea about 2-3 million years ago. Its rich content of
mostly broken and abraded fossilised shells indicates a highly energetic marine
and atmospheric environment in which material from the sea bed was repeatedly
swept up onto contiguous shorelines due to strong winds and associated wave
action. During this period the molluscan shells of a northern origin become
increasingly more numerous at the expense of southern ones. The Red Crag
deposits can be traced along the Suffolk coast from Walton-on-the Naze to
Aldeburgh with the Norwich Crag deposits occurring abruptly north of the latter
site.
The earliest scientific account of fossils contained in the Red Crag was made by
the naturalist-geologist, Samuel Dale (1659-1739) in the appendix of the topic,
The History and Antiquities of Harwich and Dovercourt, first collected by Silas
Taylor, and now much enlarged, with notes and observations relating to natural
history, London, 1730 (Challinor
1971
). Dale based his account on a letter to the
Philosophical Transactions of the Royal Society in which he commented on the yet
to be named Red Crag formation as follows:
The same strata of sand, and fragments of shells, with the same fossils imbedded [the Red
Crag], are to be found at Walton Ness on the other side of the Æstuarium [Dovercourt
Bay], which is 5 or 6 miles broad from Harwich, as likewise at Bawdsey Cliff in Suffolk,
which is 8 or 9 miles distant, and in other cliffs on that shore, where I have met with them
(Dale
1704
-1705).
This observation indicated that Dale was aware of notable exposures of the Red
Crag in the cliffs of northeast Essex and south Suffolk, later investigated by
Harmer (Figs.
3.6
and
3.7
).
Dale included two plates of the Harwich Cliff in his topic and four figures
illustrating fossils he had described in the text. In the preface Dale acknowledged
that the basis of the topic had been written by Taylor in about 1676. Following
Taylor's death in Harwich 2 years later, Dale obtained and edited the manuscript
with a view to its publication. Although the text, comprising 255 quarto pages, was
