322 HARMER : THE PLEISTOCENE DEPOSITS OF EAST ANGLIA. 
latter may be the sedimentary deposits of an extra-glacial 
lake. 
The facts here given may possibly throw some light, however, 
on one of the most interesting problems of East Anglian geology. 
The Lower Glacial beds of the country to the north of 
Norwich are overlain by a great sheet of sand (Middle Glacial), 
which forms heaths immediately to the north of that city. The 
Chalky Boulder-clay of East Suffolk and South-east Norfolk 
(Upper Glacial), on the other hand, is underlain by a similar 
deposit, which extends southwards into Essex, though it becomes 
more gravelly in that direction. It differs from the sporadic 
masses of sand associated with the glacial clays of the North of 
England, in forming a more or less persistent deposit, and 
occupying generally a definite horizon. In our survey of East 
Anglia, Wood and I found no difficulty in mapping it over an 
extended area.* Its stratigraphical position is shown in Fig. 2. 
a map of the Flegg Hundred, near Yarmouth, where these 
sands rest on the Lower Glacial brickearth, and are overlain 
by the Chalky Boulder-clay. 
The Middle Glacial sands attain in places a considerable 
thickness, nearly 70 feet in Mid-Norfolk, and more than 50 feet 
in East Suffolk, and are often much false-bedded. 
At a number of localities near Yarmouth, they were found 
to contain fossils, many of them boreal or Arctic, the fauna 
having at the same time a decidedly recent facies, Tellina balthica, 
the characteristic shell of the latest zone of the Crag and of the 
Lower Glacial beds, being one of the most common species. f 
With hardly an exception the mollusca of the Weybourne 
Crag have been found also in the Middle Glacial sands. Twelve 
species of marine Ostracoda, which Messrs. Brady, Crosskey, and 
Robertson considered to be generally of an Arctic character, 
were also obtained from the same deposits. J 
* See our Map published in the Supp. to the Mollusca of the Crag, 
Pal. Soc, 1872, and afterwards in Q. J. G. S., Vol. Hi., PI. XXXV. 
t About 100 species of mollusca are known from the Middle Glacial 
sands ; a list of the more important is given in my paper in the Proc. 
Geol. Assn., Vol. xvii., p. 460, 1902. 
t Pal. Soc, 1874, p. 103. 
