GEOLOGY 



are used not only for building hovels with the aid of a mortar of moist 

 clay, but they are used with advantage in dwelling houses, as when faced 

 with bricks the thick walls make a dry house, cool in summer and warm 

 in winter. The stones in the Boulder Clay are sometimes used for road- 

 mending in areas where gravel is scarce. 



The presence of lignite or bituminous shale in the Boulder Clay has 

 led at times to fruitless searches for coal, as near Framingham Pigot. 



Water is sometimes obtained from sandy and gravelly seams and 

 beds in the Boulder Clay, and occasionally it is of an artesian character, 

 being pent up beneath the clayey drift. 



A petrifying spring, deriving its calcareous matter from the Chalky 

 Boulder Clay, occurs at Burgh Apton, and a mineral water has been 

 advertised as the Shelfanger Spa, near Diss. The more clayey varieties 

 of the Chalky Boulder Clay form the heavier lands of Norfolk ; the strong 

 loam or 'clay marie ' of Hethel, Mulbarton, Long Stratton, Pulham and 

 Tivetshall (where the clay is from 50 to 90 feet thick). Beans and wheat 

 are cultivated with advantage, while primroses flourish in the banks and 

 line the ditches. Much of the country has a park-like aspect owing to 

 the strong well-timbered hedgerows, the broad strips of grass land which 

 border the roads, and the numerous greens and commons. 



It is by no means easy to separate the gravels and sands known as 

 Plateau Gravels from the sands and occasional gravels which underlie the 

 Boulder Clay, and have been termed Middle Glacial. The two groups 

 come together near Cromer in the sand and gravel hills which extend 

 from Paston to Weybourne and Holt, where they form a bold and 

 picturesque range of hills bordering the sea. Here the coarser upper 

 gravel cuts into the lower sands in places. They form the wooded 

 ground, occupied mostly by fir plantations at Felthorpe and Horsford ; 

 and in West Norfolk they constitute heathy tracts, rabbit-warrens, and 

 sheep-walks. Some of the gravels contain large rounded flints about the 

 size of old-fashioned cannon balls, and were termed ' cannon-shot gravels ' 

 by S. V. Wood, jun. These are the gravels which have been extensively 

 dug on Mousehold, and were formerly used for paving streets in Norwich 

 where they are still known as cobbles or ' petrified kidneys.' Occasional 

 Paramoudras occur in these gravels, and they contain many flint-casts 

 and moulds of Chalk fossils. 



The boulder-gravels occur at Poringland and Strumpshaw, at 

 Tharston Furze Hill, Hapton and Wymondham, at North Elmham, 

 Tatterset, Hempton Common near Fakenham, Syderstone and Docking. 



Near Docking the gravel contains hard chalk as well as flint, and 

 blocks of it cemented by iron-oxide have locally been used for building. 

 In many of the localities the flint boulders have been used for building- 

 purposes. The round church towers of Norfolk were mostly built of 

 such materials, there being little or no freestone in the county suitable 

 for corner-stones. 



These coarse gravels probably resulted from the melting of the ice 

 which brought the materials of the Chalky Boulder Clay. The gravels 



21 



