GEOLOGY 



at Yarmouth ; they are exposed beneath the Glacial Drifts on the coast 

 from Happisburgh to Weybourne, and inland along the borders of the 

 Bure, Yare, Wensum, and Waveney. They extend as far west as Guist, 

 and as far south as Harleston, Ditchingham and Aldeby. In the Bure 

 valley they rise occasionally into islets in the Alluvium, know^n as Holms 

 or Holmes, as St. Benet Holme. They comprise a variety of deposits to 

 which many local names have been given ; but broadly speaking they 

 may be separated into a lower division, the Norwich Crag Series, and an 

 upper series the Cromer Forest Bed. 



The Norwich Crag Series consists of sand and pebbly gravel with 

 seams of laminated clay, and with patches here and there of Crag shells, 

 the common fossils being many of them species now existing, such as the 

 cockle {Cardium edule), the mussel {Mytilus edulis), and the periwinkle 

 {Littorina littorea), while others are extinct forms. 



The series varies in thickness from 30 feet near Norwich to 95 feet 

 at Harleston. The beds may be thicker also under Yarmouth, as from the 

 evidence of well-borings we find the Crag to become thicker towards the 

 North Sea. 



In appearance it may be likened to an extensive raised shallow sea- 

 bed ; it includes deposits laid down in shoals and sand-banks, with 

 channels eroded by currents. The incoming of freshwater, probably from 

 streams entering sandy bays, has influenced some of the mollusca, as may 

 be seen in the varieties and monstrosities of the purples and periwinkles, 

 and also in the remains of land and freshwater mollusca. The bands of 

 laminated clay, as remarked by Mr. Reid, seem to indicate more estuarine 

 conditions.^ 



Borings of Pholas and Annelides are occasionally seen in the Chalk 

 platform on which the Crag lies ; and abundant remains of barnacles, of 

 Pecten opercularis and Tellina crassa are there met with in its lowest beds. 



The oldest portions of the Crag which have been termed Fluvio- 

 marine on account of their containing remains of land and freshwater 

 shells, are best seen at Bramerton and Thorpe near Norwich, localities 

 from which the majority of the well-known fossils have been obtained. 

 At one pit at Bramerton the Crag is locally as red as much of the Red 

 Crag in Suffolk. 



At the base is a Mammaliferous stone-bed, a layer from i foot to 

 18 inches thick, of unworn and little worn flints, derived from the 

 Chalk, together with pebbles of quartz and quartzite, in and above which 

 bones and teeth of deer, antelope, mastodon, and Elephas antiquus (in- 

 cluding portions of the tusk of that elephant) have been found. This 

 stony base is not however confined to the same geological horizon, it 

 underlies newer stages of the Crag, and was evidently a marine basement- 

 bed formed as the Crag sea encroached on the Chalk area, for we have 

 evidence that the lower stages of the Crag were overlapped by higher 

 strata as we proceed northwards and north-westwards. 



* 'Pliocene Deposits of Britain ' {Geol. Survey), 1890, p. 131 ; see also F. W. Harmer, 

 Quart. "Journ. Geol. Soc, vol. lii. p. 768. 



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