143 
WEYBOURN CRAG. 
Chalk; or where the clay thickens it seems to have increased at the 
expense of the shelly Crag. The evidence is thus not perfectly 
Fig. 35. 
Section at the Lime-Kiln, Guisf, 
(H. B. Woodward.) 
e. Brown stony, and sandy clay. 
d. Chalky and sandy Boulder Clay, bedded at base, 5 to 6 feet. 
c. Grey and buff micaceous sand and shingle, and laminated clay, with nodules of 
“ race,” 5 to 10 feet. 
b. Stone-bed. 
a. Chalk with flints. 
satisfactory, for in this area the only grounds for the separation of 
the two horizons, is the supposed exclusive occurrence of Tellina 
halthica in the upper one. The list of mollusca from the upper 
bed in the Bure Valley is much too small to allow of any useful 
comparisons. 
Failing vertical superposition, for the older deposit appears to 
be entirely absent in the continuous exposures of Crag between 
Cromer and Weybourn, we are compelled to fall back on the 
palseontological evidence, and to rely almost entirely on Lyell’s 
test of the per-centage of recent mollusca contained in the beds. 
A much larger number of species, fortunately, has been obtained 
from the sections on the coast than from the Bure Valley, and 
though, perhaps, the number may still be too small to allow us 
to speak of the relative age of the deposits as being settled beyond 
further question, yet the direction in which the figures point is 
unmistakeable. 
From the Weybourn Crag there have now been obtained 53 
species and marked varieties of marine mollusca. Of these, five 
are extinct, showing a per-centage of 10*6, compared with 15*5 
and 16*0 from the Chillesford and Fluvio-marine Crags respec¬ 
tively. But as the total number of species known from the 
Weybourn Crag is still considerably smaller than that from the 
older beds, and forms dying out are likely to be represented by 
