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 GEOLOGY intervals to near Massingham. Again the Wensum, whose ordinary source is at Wickend Pond, north of Tatterset, rises nearer to Barmer in very wet weather. Among the noteworthy Chalk springs are those of Marham, which are utilized for the water-supply of Wisbech and some of the Fenland villages ; while the springs thrown out by the Gault east of Appleton are used for the supply of water to Sandringham House. Springs which issue below high-water mark from the Chalk at Wells gave rise to the name of the town ; while the wishing wells at Walsingham are also derived from the Chalk. In West Norfolk the natural pools of water known as Meres, which occur on the heaths of Roudham and Wretham, indicate the plane of saturation of the Chalk, and may partly owe their form to dissolution of the Chalk. Some have no apparent outlet, others lie along the course of the Wissey. Diss Mere is probably of the same character. It lies in the Glacial sands, but the water is evidently derived and maintained by Chalk springs.^ The surface of the Chalk at different localities has been subject to local erosion by the action of carbonated water. Thus great ' pipes,' sometimes 20 feet deep and 5 feet across, have been formed, and these are in places filled with gravel and sand or other accumulations which have subsided into the cavity formed. This process may be a slow one, but it sometimes occurs suddenly.^ The Chalk formation as a whole indicates a deep sea — the material being for the most part the calcareous mud or ooze which has been produced by the decay of various organisms, many of them of the lowly type of Foraminifera. READING BEDS AND LONDON CLAY Although Eocene strata are nowhere in Norfolk exposed at the surface it is appropriate here to consider them, because locally they come in direct succession to the Chalk, despite the break in time between the two groups. Indeed the Eocene deposits may be said to be as nearly connected with the Chalk in Norfolk as they are in other parts of England, for although we have no distinct representation of the Thanet Sands, which form the lowest Eocene division in Essex and Kent, yet at Trimingham we find a higher stage of the Chalk than is known elsewhere in this country. The Eocene strata have been proved only in one spot, in a boring for Lacon's Brewery, at Yarmouth, where beneath 120 feet of superficial deposits and Crag there were found 3 1 o feet of London Clay and 46 feet of green sands and grey clays belonging to the Reading Beds.' It is of Diss,' etc. 1884, p. 3. vol. iii. p. 641. ' Prestwich, Quart. Journ. Geol. Soc, vol. xvi., p. 450. II
 * F. J. Bennett, 'Geology of Attleborough,' etc. {jGeol. Survey), 1884, p. 17 ; 'Geology
 * J. Evans, Geol. Mag., vol. v. p. 445 ; H. B. Woodward, Trans. Norf. Nat. Soc,