Gcolo(jij of Norfolk. 
463 
dered as belonging rather to the upper drift than to the till. On 
the slope of the western escarpment portions of deep beds of till 
again occur at the heads of some of the valleys, but from the 
steepness of the slope it has been more denuded than in the 
more level districts on the east ; and the greater portion of the 
western valleys have been swept clean of the detrital deposits, 
the chalk having only a thin covering of sand. In the lower parts 
of these valleys the till is covered by the alluvial deposits. 
The upper surface of the till is very irregular in the Cromer 
cliffs, as shown in Section III., its depth varying from less than 
10 to 70 or 80 feet. 
In the river sections of the southern and central parts of the 
county, and in the pits where the till rests on the sand of the 
crag, it is seldom that more than 10 feet of it are exposed, but 
large portions of its upper part have evidently been removed by 
denudation. Where it is deep it has not been sunk through. In 
the section of strata penetrated in sinking a well at Diss, as re- 
corded by Mr. John Taylor,* its depth appears to have been 
about 50 feet. 
6. The Upper Drift. 
The till is generally said to be unstratified, but improperly as 
regards that of Norfolk, because in the least stratified portions 
alternations of deposits are marked by irregular seams of frag- 
mentary chalk. These are best seen either in fresh sections, or 
when masses of the clay have been exposed to the wash of the 
sea. The face of the cliff is in general covered by a crust 
brought down by the rain, which conceals the stratification. In 
the upper drift, however, stratification is much more decided, 
consisting of alternating beds of sand, gravel, loam, and coarse 
shingle. The till passes upwards into laminated blue clay ahd 
silt, which again pass into the yellow sands of the upper drift, 
containing large masses of fragmentary chalk. 
The till occurs but once, and that at the commencement of 
the period of the drift ; after which, the peculiar causes, what- 
ever they were which produced it, ceased. In the upper drift 
there are several alternations of the fragmentary and reconstructed 
chalk. These, in East Norfolk, constitute a large portion of the 
"marl" which has been so extensively used for the improvement 
of its light soils. It is found in some cases mixed with a variable 
proportion of blue and yellow clay and sand, in others it is suffi- 
ciently pure to be burned for lime. Among the numerous in- 
stances of lime-kilns situated on these beds of transported and 
* Lond. and Ed. Phil. Mag., vol. v. p. 295 ; and Proc, Geol. Sec. vol. 
ii^ p. 93. 
