Geology of Norfolk. 
449 
sion that they were formed not during one epoch, but many ; that 
they had been shot off the Hanks of mountain chains during suc- 
cessive movements oi elevation, and that it was impossible to dis- 
tinguish the detritus of different periods thus blended together. 
In this spirit of hasty generalisation, it has been too much the 
custom with those who have undertaken the investigation of the 
superficial deposits to think that they have accomplished the task 
by bestowing on them a new name. Hence, besides those of De- 
trital Deposits, Diluvium, Post-tertiary Strata, and Loose Cover- 
ing of the Earth, their many synonyms of Northern Drift, Erratic 
Block Group, Boulder Formation, Terrains de Transport, Mud 
Cliffs, Tertiary Strata, Post-Pliocene Strata, Moraines, and Gla- 
cial Formation. The glacial theory of Agassiz has again attracted 
attention to them, and whenever they shall be studied with the 
same diligence and patience which have been bestowed upon 
other departments of geology, there can be no doubt that they 
will be studied with equal success, and that a rich harvest will be 
reaped as valuable for its economic results as for the important 
chapter which will be opened in the history of the earth. 
The base of these deposits in Norfolk consists of a great sheet 
of chalk with an undulating and waterworn surface which dips 
under the sea to the southward of east, and rising towards the 
interior, attains its greatest elevation along a line which ranges 
from Lopham Ford, between the sources of the Waveney and the 
little Ouze, by Swaffham to Brancaster, and constitutes the water- 
shed of the county, known as the Downs of Norfolk. On the east- 
ern side of the watershed the surface consists of deposits of the 
erratic block group, varying in depth from less than three to more 
than three hundred feet. Within this area is a tract in which the 
Norwich, or mammalian, crag is interposed between the chalk and 
the erratic deposits. It is bounded on the north, the east, and the 
south, by the Ocean and the marshes of the Yarmouth estuary, 
south of which it reappears in Suffolk. Its western boundary is 
an irregular, and not very well ascertained line, which may be 
described, in general terms, as ranging from Weybourne to some 
point between Bungay* and Diss, ramifying among the hollows 
in the chalk, which appears to have broken with islands and pro- 
montories the continuity of the sea in which the crag was depo- 
sited. Beneath the greater portion of the larger area east of the 
* In the map accompanying Woodward's ' Geology of Norfolk,' Bungay 
is made the western boundary of the crag on the south. That is the 
furthest point in which shells have been observed in it. It is there seen 
covered by the till of the erratic block group. I have traced the same 
kind of sands, holding the same relative position to the till, but without 
fossils, considerably to the westward of Harlestone. They are also seen 
in the upper part of the valley of the Wensum, near Svvanton Morley. 
