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Show 270 SILTING UP OF ESTUARIES-SUBMARINE FORESTS. across the whole entrance of the ancient estuary, and obstructing the ino-ress of the tides so completely, that they are only ' admitted by the narrow passage which the river keeps open, and which has gradually shifted several miles to the south. The tides at the river's mouth only rise, at present, to the height of three or four feet. By the exclusio~ of the sea, thousands of acres in the interior have become cultivated lands; and, exclusive of smaller pools, upwards of sixty fresh water lakes have been formed, varying in depth from fifteen to thirty feet, and in extent from one acre to twelve hundred*. The Yare, and other rivers, frequently communicate with these sheets of water; and thus they are liable to be filled up gradually with lacustrine and fluviatile deposits, and to be converted into land covered with forests. When the sea at length returns (for as the whole coast gives way, this must inevitably happen sooner or later), these tracts will be again submerged, and submarine forests may then be found, as along the margins of many estuaries. 'Ve may easily conceive that such natural embank· ments as those thrown by the waves, and subsequently raised by winds, acrosR the entrance of this river, may so shut out the tide, that inland places may become dry which, on the breaching of the barrier, might again be permanently overflowed even at low water ; for the tides are now so depressed, even outside the barrier, that the river is almost in the condition of one which enters an inland sea. Were high tides to recur, tl1e fresh-water would be ponded back during the flow, and would perhaps not entirely escape during the ebb. It has been observed, by Dr. Fleming, that the roots of the trees in several submarine forests in Scotland are in lacustrine silt. The stumps of the trees evidently occupy the position in which they formerly grew, and are sometimes from eight to ten feet below high water mark. 'fhe horizontality of the strata and other circumstances, preclude the supposition of a slide, and the countries in question have been from time immemorial fr:e from violent earthquakes, which might have produc~d sub:tdences. He has, therefore, attributed the depresswn, with much probability, to the drainage of peaty soil on the re~oval of a seaward barrier. Suppose a lake (like one of those m the • Taylor's Geology of East Norfolk, p. 10. LOSS OF LAND ON THE SUFFOLK COAST, 271 valley of the Yare,) to become a marsh, and a stratum of v.e getable matter to be formed on the sur1ra ce, of su ffi c1· ent d en-sity to support trees. Let the outlet of the marsh be elevated a few feet only above the rise of the tide. All the strata below the 'lfelv e· dl of the outl.e t wou.l d be. kept const an tl y we t or m· a semi m state, J:>ut If the tides nse in the estuary, and the sea encroaches, . p.o rtwns of the gained lands are 8 wep t away, an d the extretmties of the aJluvial and peaty strata, whereon the forest grew, are exposed to the sea, and at every ebb tide left dry to a depth equal to the increased fall of the tide. Much water, formerly prevented from escaping by the altitude of the outlet, now oozes out from the moist beds,-the strata collapse a~d 1 th 1 e .suhrfac~ of the morass instead of remaining at its ori"" gma leig t, smks below the level of the sea *. ~ armouth does not project beyond the general line of coast winch has been rounded off by the predominating current from the n.o~t.h-west. It must not be imagined, therefore, that the acqm.sitl?n of new land fit for cultivation in Norfolk and Suffolk .mdiCates any permanent growth of the eastern limits r0 f our Island, to compensate its reiterated losses. No delta can form on such a shore. The cliffs of Suffolk, to which we next proceed, are some~ h~t less elevate~ than those of Norfolk, but composed of similar accumulatwns of alternating clay sand and 1 F G 1 · ' , grave . rom or eston .m Suffolk, to within a few miles north of Low~stoff, the chffs a:e slowly undermined. Near the lastmentiOned to.wn, there Is an inland cliff about sixty feet high, the talus be~ng covered with turf and heath, between which an? the sea Is a low, flat tract of sand, called the Ness, which fams slowly on the sea. It does not seem difficult to account t~r ~he retreat or the sea at this point from its ancient limits, the ~s~ of the mland. cliff. About a mile off Lowestoff lies 'l'~e c 0 m Sa.nd, th.e highes.t part of which is dry at low water. . b urrent m the mtervemng passage, called Lowestoff Roads r ls 1 a a1ck-wat~r, wherein the tide, instead of obeying the generai u e a onO' this co t · 1 1 h o as , runs mne 1ours towards the north and on y t ree towards the south. Here, therefore, we ha~e an * See two papers S b . Roy. Soc. Edin 1 o.n u ;anne Forests by the Rev. Dr. Fleming, in the Trans. March, 1830 . ., vo, Ix., p. 19, and Quarterly Journ. of Sci., No._l3, new series, |
