434 EXCURSION TO ALDEBURGH, WESTLETON, AND DUNWICH. WHITSUNTIDE, MAY 29TH TO JUNE 1ST, 1898. Directors: W. WHITAKER, F.R.S., PRES. G.S.; F. W. HARMER, F.GS.; AND E. P. RIDLEY, F.G.S. Excursion Secretary: BEDFORD McNEILL, A.R.S.M., F.G.S. (Report by F. W. HARMER.) THE members left Liverpool Street Station on Saturday. May 29th, by the 11,45 a.m. train for Aldeburgh. On arrival, they proceeded to the Brudenell Arms Hotel, the head­ quarters. A short excursion was made during the afternoon to the hamlet of Slaughden, half a mile south of Aldeburgh, to inspect the damage caused by the high tide of November, 1897. It will be seen by reference to the map (Fig. 1) which, with other illustrations, has been reprinted from a paper by the writer," by the kind permission of the Council of the Geological Society, that the river AIde approaches Slaughden at right angles to the coast, and the estuary, of which the present stream is the shrunken representative, must formerly have communicated with the sea in that direction. The travel of the beach, which on the eastern coast of England is from north to south, that is, in the direction of the currents attending the flowingtide, caused, however, the accumulation of a bank of shingle across the mouth of the estuary, and this bank continuing to increase in the same direction, gradually shifted the outfall to the south. At present the river AIde enters the sea at a place called Shingle Street, 8 or 9 miles from Aldeburgh, running parallel to the coast between the two places, a narrow belt of shingle-beach and salt marsh only intervening. The high tide referred to transferred great quantities of shingle from the seaward to the landward side of the bank, rolling the pebbles over its crest, shifting the position of the bank westward, and causing it to make in places great inroads on the adjoining marshes. A number of buildings that stood im­ mediately behind the bank were wrecked or damaged by its advance. It is a hundred years since the poet Crabbe, then Rector of Aldeburgh, prophesied such a calamity in the following lines, appropriately quoted by Mr. Monckton from" The Village" : Till some fierce tide, with more imperious sway, Sweeps the low hut, and all it holds, away. One of the principal objects of the excursion to the Aldeburgh district was an examination of the zone-theory of the late Sir • Quart. ] ourn. Geoi, Soc., vol. !iv, p. 308, 1898. NOVEMBER, 1898.] EXCURSION TO ALDEBURGH, WESTLETON, AND DUNWICH. 435 S~alt' (1/ .1/ila o \, M ~ p of the main mass of the CORALLINE CRAG; ! hcwing t he posltlon of the .... arlous sections and borii\.1) alluded to In t his paper. T /;( c/oflrd a rra ""p,..-sm!s f,~ a ! c.r.·..·r~·J t')' t/:e C"r.:tlillc C,."g'. -, FIG. I. NOTE.-The posItIon of pit 30 should have been indicated just below the letter K (in "Kiln") due west of Aldeburgh. (Reprinted by permissio» Iron» The Quarterly Journal of the Geological Socieiy.) 436 EXCURSION TO ALDEBURGH, WESTLETON, AND DUNWICH. Joseph Prestwich, the correctness of which has recently been challenged by the writer." It has been held by all authorities to the present time that the Coralline Crag may be divided into a lower portion, composed of whitish, incoherent, calcareous sands, with frequent beds of shells, and an upper bed of indurated ferruginous rock. Prestwich adopted these divisions, but he believed that the lower part of the formation might further be separated into five distinct and continuous zones, representing great physiographical changes, induding a gradual submergence of the Crag area to a depth of 500 or possibly of 1,000 feet, and alternations of climate by which at one stage the winter tempera­ ture of Northern Europe became sufficiently cold to bring floating ice from Scandinavia or the Ardennes to the shores of England. The writer has given in the paper already referred to the reasons which induce him to differ from these views. So far from admit­ ting that the Coralline Crag can be divided into a number of zones, he now believes that the distinction between the shelly sands of Gedgrave and Sudbourne, and the ferruginous rock of Iken and Aldeburgh, is more apparent than real, and that the one is merely an altered condition of the other. With the exception of that of the basement bed, the material of the Coralline Crag is practically identical throughout, being almost entirely organic, formed of the comminuted remains of polyzoa and mollusca, with seams of perfect specimens of such organisms, and it must all, therefore, have originated under similar conditions; probably as a bank, in water of no great depth, parallel to the western shore of the Crag sea, and at no great distance from it. The molluscan remains are, with very few exceptions, the drifted shells of dead animals only, differing in this respect from the contemporaneous Isocardia-beds of Antwerp, which represent an undisturbed sea-bottom, the lamellibranchiate fossils of those beds being always found double, and never arranged in layers as in the Crag. It seems probable that the Coralline Crag banks were due to currents from the south-west flowing through a strait that connected the North Sea with the English Channel, which deposited little sediment where they ran strongly, but swept up from the sea-bottom the shells of mollusca living on it, depositing them afterwards in comparatively sheltered situations where the influence of the current was less felt.j Similar conditions now obtain off the coast of Antrim and at the southern end of the Isle of Man. An interesting proof of the identity of the two kinds of Coralline Crag was pointed out in pit No. 27, at the Brick Kiln Farm at Iken, visited on the 30th (see Map, p. 435), where a lenticular patch of the deposit in its unaltered condition, crowded with perfect shells like those of the sands at Gedgrave and elsewhere, occurs in the midst of a mass of the indurated * Oua rt./ourn. Geol. Soc., vol. liv, p, ~oB. 1898. t the writer's views as to the geographical conditions under which the Coralline Crag. may hav e originated are shown in th e accompanying map (Fig. •). e-, ,.,ll'j <""l ':'I." : I' ~' , , "'!" Sleeuretl Rocks .\J.h..{.ur.:h , ~ " , • · 1 , I Jk t"u. m fl H" i ~ u . t l )l o l"lIltOlI' L_.., ... ........ ~ 1·at l ill J: " ~ On c (' ~z ::>c Q Z -t, Z~ 0 E-< (zl ~~ ~ ~ :' < , ...l ------._---- - ~;- -.-"-'" -",, "', E-<en (zl '" c ( ----------- ~ IN E :£ .,.. ---- c i>\ ::> I"l ~ Q ...l «: 0 f-< Z 0 (jj ~ o::> x r<l F IG. 2. - MAI' SHO WI NG THE APPROX IMATE WE5 TER:oi AND SOUT H ERN LIM ITS OF T HE G ERM A N O CEAN DUR ING T HE MIOCEN E, A ND AT T HE CO MMENCEMENT AND TOWARDS THE END OF Til E DIESTIEN PERIO D, AND THE r-ossrai.s C0 1-l OlT I')NS UN DER wrnc« T HE CORALLI NE CRAG MAY HAVE ORIGINATED. ~ ica l (Reprinted by pen/liss;on from The Quarte rlf f aurna i of ti,e Ge o lo. S ociety .) 438 EXCURSION TO ALDEBURGH, WESTLETON, AND DUNWICIJ. ferruginous rock bed. Visitors to this spot are particularly requested to leave untouched this interesting patch of Crag, probably the only one of the kind in existence. The shells included in it can easily be obtained near Orford, and in a better state of preservation. In other places, as at pits 31 and 33 at Aldeburgh, visited subsequently, layers of molluscan fossils are to be observed, but in the form of casts only, the calcareous matter of the shells having been removed by the infiltration of acidulated water, which has at the same time dissolved a portion of the glauconite usually present in the shelly sands, and produced the ferruginous and indurated condition of the altered Crag. In pit No. 24, seams, a few inches in thickness, of reef-build­ ing polyzoa were noticed, extending horizontally across the section. It is suggested that these seams, which occur in places only, were due to the temporary diversion of currents, by which the accumulation of comminuted material ceased for a time at certain spots, so that polyzoa could there establish themselves, but they would afterwards be smothered and unable to exist when the returning currents brought over them again a new layer of the fine calcareous mud. At pit 25, now obscure, the position of the overlying Red Crag was pointed out, and at the disused brick-field, 26, a patch of Chillesford Clay was observed at one part of the section. MOllday, May 3Ist, was devoted to the examination of the exposures near Aldeburgh . Commencing the day's excursion at the pumping-station of the Water Works Co., where the arrange­ ments for supplying the town with water were explained, the party visited successively pits 30, 34, 31, and 33, where a number of specimens of polyzoa, some echinoderms, and many casts of mollusca were obtained. Mr. P. F. Kendall pointed out many years ago * that the preservation of the polyzoa, and of a few mollusca such as Pecten, Mytilus, and Terebratuia, in the indurated Crag was due to the fact that the shells of such organisms are composed of carbonate of lime in the form of calcite; aragonite, of which the tests of most mollusca consist, being more readily acted on by water containing carbonic acid.