Fig. 117: Natica helicoides Chillesford and Aldeby Beds.—It is in the counties of Norfolk, Suffolk, and Essex, that we obtain our most valuable information respecting the British Pliocene strata, whether newer or older. They have obtained in those counties the provincial name of “Crag,” applied particularly to masses of shelly sand which have long been used in agriculture to fertilise soils deficient in calcareous matter. At Chillesford, between Woodbridge and Aldborough in Suffolk, and Aldeby, near Beccles, in the same county, there occur stratified deposits, apparently older than any of the preceding drifts of Yorkshire, Norfolk, and Suffolk. They are composed at Chillesford of yellow sands and clays, with much mica, forming horizontal beds about twenty feet thick. Messrs. Prestwich and Searles Wood, senior, who first described these beds, point out that the shells indicate on the whole a colder climate than the Red Crag; two-thirds of them being characteristic of high latitudes. Among these are _Cardium Grœnlandicum, Leda limatula, Tritonium carinatum,_ and _Scalaria Grœnlandica._ In the upper part of the laminated clays a skeleton of a whale was found associated with casts of the characteristic shells, _Nucula Cobboldiæ_ and _Tellina obliqua,_ already referred to as no longer inhabiting our seas, and as being extinct varieties if not species. The same shells occur in a perfect state in the lower part of the formation. _ Natica helicoides_ (Fig. 117) is an example of a species formerly known only as fossil, but which has now been found living in our seas. At Aldeby, where beds occur decidedly similar in mineral character as well as fossil remains, Messrs. Crowfoot and Dowson have now obtained sixty-six species of mollusca, comprising the Chillesford species and some others. Of these about nine-tenths are recent. They are in a perfect state, clearly indicating a cold climate; as two-thirds of them are now met with in arctic regions. As a rule, the lamellibranchiate molluscs have both valves united, and many of them, such as _Mya arenaria,_ stand with the siphonal end upward, as when in a living state. _Tellina balthica,_ before mentioned (Fig. 116) as so characteristic of the glacial beds, including the drift of Bridlington, has not yet been found in deposits of Chillesford and Aldeby age, whether at Sudbourn, East Bavent, Horstead, Coltishall, Burgh, or in the highest beds overlying the Norwich Crag proper at Bramerton and Thorpe. Fig. 118: <i>Mastodon arvernensis,</i> third milk molar, left side, upper jaw: grinding surface. Norwich Crag, Postwick, also found in Red Crag, see p. 197.