CROFTS : NOTES OX ALEXANDRA DOCK EXTENSION, HULL. 251 
the Holderness Cliffs, together with detritus brought down the 
rivers flowing into the Humber, it is advisable to suspend judgment 
until a series of exhaustive experiments put the matter beyond 
dispute. This warp is of course identical in composition with the 
warp now in course of formation along the shores of the Humber. 
There is evidence of a dip in the Chalk underlj^ing the 
district, corresponding with the basin of the river Hull, and the 
ancient chalk cliffs may possibly be east of the river. The glacial 
deposits extend from the sea on the east, on to the edge of the 
Wolds on the west, the depression in the valley of the Hull 
being filled with the warp. The glacial gravels bear a strong 
resemblance to those adjoining the ancient meres of Holderness, 
which do not contain fossil shells, and have the appearance of 
being formed in a similar manner. 
There is a gravelly bed extending over a great part of 
Holderness between the boulder clays known as the " purple ' 
and " Hessle," filling channels of varying depth in the so- 
called "purple" clay, the ancient mere beds being apparently 
very large channels along which at one time strong currents have 
flowed, the percolation water deepening the channel and letting 
down the gravels. The " purple '"' clay where the gravels are 
most developed is generally attenuated, and sometimes missing 
altofjether, so that this bed may fairly be connected with that 
division. I am inclined to think that as the Kelsey Hill gravels 
occupy a similar position between the "Hessle" and "purple" 
clays, they belong to the same period as this great gravel bed, 
and that the presence or absence of shells is due to the position 
of the old beach from which they are probably derived. These 
gravels are well exhibited in the excellent coast sections. 
The peat bed, although now 13 ft. below high water level 
of ordinary spring tides, must at one time have been above the 
high water level, when the plwsical appearance of the district 
must have considerably differed from its present aspect, but 
the interesting field this opens out can scarcely be touched upon 
here. Take one point alone : the Humber channel at the present 
time is of no great depth in places, and I am inclined to think 
