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, known 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. G^ol. Soc, vol. lii. p. 768. 13
