XXX SUPPLEMENT TO THE CRAG MOLLUSCA. 
The rest of the Post-glacial formations shown in the map and sections under the 
number 11, are with some exceptions, (among which must be included beds wherein Cyrena 
Jluminalis occurs, such as those at Stutton on the Stour estuary, and at Gedgrave near 
Orford, regarded by us as belonging to the older part of this period,) probably 
newer than these marine gravels, and belong to the later part of the Post-glacial period. 
In the preceding Yorkshire Coast section the earlier Post-glacial series, the Hessle sand 
and clay (7 and e), are excavated or removed to give place to numerous later beds (/) of 
sand and gravel, which are of considerable thickness, and some of which contain freshwater 
Mollusca. It is clear from this coast section, therefore, that extensive beds, especially 
river gravels, accumulated over the north-east of England after the land had emerged from 
the Hessle clay re-depression; and to these we consider the principal part of the Hast 
Anglian Post-glacial Valley beds, which are shown in the map, under the number 11, 
belong.’ 
The recent alluvium, shown in the map under the figure (that of a crow flying) which 
has been adopted in their maps by the Geological Survey to distinguish these deposits, 
is mainly due to that considerable depression anterior to historical times, which buried 
so much forest ground all round the English coasts. ‘This last depression brought the sea 
water into valleys which during the preceding (later Post-glacial) period were dry and 
forest-covered ; and filling them, has given rise to the Broads of Hast Norfolk. The same 
depression has produced the wide flats of alluvium which fill so much of the valleys of the 
Waveney, Ant, and Yare, in Hast Norfolk, by silting up the lower parts of these valleys with 
modern estuarine mud, which was found at Yarmouth, in a well boring, to be 170 feet 
in thickness.? 
The rest of the recent deposits consist of shingle, such as the great bank which shuts 
in the Alde from the sea at Orford, or of blown sand, which at Lowestoft has buried the 
sea cliff, and with some deserted foreshore has produced new land called the Denes. 
S. V. Woop, Jun. 
F. W. Harmer. 
February, 1872. 
N.B.—tThe lithographic map having been reduced to one fourth the original scale, 
from a survey made on the one inch Ordnance sheets, those who may have occasion to 
use it for field purposes will find it convenient to employ these sheets, (which are of very 
shading and number as the Post-glacial gravel (10), but it, in fact, passes over that gravel where the cliff 
is highest (under the Ruins), and where a small portion of the clay No. 9 remains iz siti, but the two 
patches, numbered 10, capping the southern half of the section, consist entirely of this loam. 
1 Sections of the Crag and Glacial beds along valley sides often show a Post-Glacial gravel over them, as, 
e. g., Sections IX, X, XI, and XIV. It would, however, be scarcely possible to map all these patches, and if 
done their representation would obscure that of the older beds. 
2 See Prestwich in ‘ Quart. Journ. Geol. Soc.,’ vol. xvi, p. 449. 
