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 



* F. J. Bennett, 'Geology of Attleborough,' etc. {jGeol. Survey), 1884, p. 17 ; 'Geology 

 of Diss,' etc. 1884, p. 3. 



* J. Evans, Geol. Mag., vol. v. p. 445 ; H. B. Woodward, Trans. Norf. Nat. Soc, 

 vol. iii. p. 641. 



' Prestwich, Quart. Journ. Geol. Soc, vol. xvi., p. 450. 



II 



