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Published online by Cambridge University Press: 01 May 2009
The Suffolk Crags.—There are few deposits in this country which form so admirable a field for study as the Crags of Suffolk. Unique as to age, the sole representatives in England of the great Pliocene deposits of Europe, it becomes a matter of very high interest to identify them in any way with particular strata in other countries. The lowest of these Crags occurs in small patches over an area of about eighty square miles, and consists of either loose or compact light-coloured sand, alternating with bands of Polyzoa, which sometimes form a kind of limestone. From this Crag 299 species of Mollusca have been obtained: of these, 148 are extinct, 151 are still living. This so-called ‘Coralline Crag’ lies on London Clay, and is seldom more than 20 feet in thickness. The ‘Red Crag,’ so called from its iron-stained appearance, is an irregularly stratified deposit, composed of rather coarse sand and fragments of shells, abounding also in more perfect remains, but very rarely affording the valves of Conchifera, opposed or in sitû. It extends over a larger area than the Coralline Crag, abont 200 square miles, part of which is in Essex. The Red Crag, rarely exceeding 20 feet in thickness, in most localities rests on the London Clay, the Lower Crag having probably been denuded: it is occasionally, however, found resting on the latter. At the base of both Crags, when resting on the London Clay, a deposit of rounded concretionary nodules, derived from and containing the fossils of the London Clay, is found, and is worked for the nodules, which in great part consist of phosphate of lime, and are manufactured into manure. Associated with these nodules, are teeth of Mastodon, Rhinoceros, and other Mammals,† which have been derived perhaps from earlier Pliocene, perhaps from Miocene strata, and are similar, in some respects, to those obtained at Eppelsheim in Germany. In addition to these, there are the remains of large Cetacea, much worn and rolled, as well as the teeth of the large Carcharodon and Oxryrhina. These are probably the remains of a former Pliocene deposit, broken up like the Miocene beds at the beginning of the Crag era. Similar vertebrate fossils and phosphatic nodules are also dispersed at intervals in the higher strata of the Red Crag. Their occurrence here has led to much confusion, since they have been, and still are by many, regarded as indigenous to the Crag.
page 103 note * The most important notices and memoris that have been written on the Crags of Suffolk and Essex are—by Mr. Charlesworth, Proceed. Geol. Soc. 1835, vol. ii. p. 195;Google Scholar Phil. Mag. 1835, 3rd Ser., vol. vii. pp. 81, 465;Google Scholar Reports Brit. Assoc. 1836, Trans. Sect. p.84;Google Scholar by Sir Lyell, C., in his ‘Principles’ and ‘Elements of Geology’, and in the Mag. Nat. Hist. 1839, New Ser., vol. iii. p. 313;Google Scholar MrPrestwich, , Quart. Journ. Geol. Soc. 1849, vol. v. p. 350;Google Scholar MrWood's, S. V. Monograph of the Shells of the Crag (2 vols. 1848–1856 Palæontographical Society), and his paper on the Extraneous Fossils of the Red Crag, Quart. Journ. Geol. Soc. 1858, vol. xv. p. 32;Google Scholar and MrWood, S. V. jun., on the Red Crag, Annuals Nat. Hist. 1864, 3rd Ser., Vol xiii. Besides the Mollusca, the Cirripedia, Echinodermata, Polyzoa, Corals, and Entomostraca of the Suffolk Crag have been figured and described in the Monographs of the Palæontographical Society. The Crags of Antwerp were treated of by Sir C. Lyell in the Quart. Journ. Geol. Soc. 1852, vol. viii. p. 281, &c;Google Scholar and several papers on these deposits and their fossils are to be found in the publications of the Brussels Academy, &c. Reuss has described the Foraminifera of the Antwerp Crag in the Proceed. Vienna Acad., vol. xlii., 1860, p. 355, &c.Google Scholar
page 104 note * Of the three recognized divisions of the ‘English Crag,’ the lowest has been known as the ‘Coralline Crag’ ever since Mr. Charlesworth so named it in 1835, on account of its aboundingwith little coral-like fossils, which, however, when duly studied, were found to be Bryozoa (Polyzoa); Corals being exceedingly rare in it. ‘Bryozoan Crag’ oughit, therefore, to take the place of this common misnomer; but ‘White Crag,’ or ‘Lowest Suffolk Crag,’ are better names for this division, and already in use.—Edit. Geol. Mag.
page 104 note † It appears from the researches of Dr. Falconer, that these fossils are identical with Sub-Apennine forms: others, however, consider them of Miocene age. Whichever is the correct view, there is no doubt that the fossils are extraneous, and derived from earlier beds.
page 106 note * It is impossible to estimate correctly the depth of any of the strata, as the trench varies much in depth itself. It is in most places 9 metres (29½ feet); and a glance at the section will show the relative amount occupied by each bed.
