COLE : DESCRIPTION OF PHOTOGRAPH OF BOULDER CLAY CLIFFS. 445 
be the oldest deposit in this locality, to whichever section of clays it 
may eventually be assigned. 
It is interesting to note, in this connection, the marvellous 
vicissitude of climate which, in long-passed ages, has occurred in the 
British Isles. On the one hand we find rocks due to the growth of 
corals, which can only exist in a temperature of some 68 degrees, 
and, on the other, a super-stratum of clay, the product of intense 
glaciation Countless years, of course, intervened, but the fact 
remains. 
IV. Present Denudation. 
We come now to the present denudation. It exhibits in a re- 
markable way the effect of the rainfall in contradistinction to other 
agencies. No doubt frost has played its part, but only as a con- 
comitant of the water which forced its way into the cracks. The 
cracks were mainly produced by the heat of the sun, acting on clay 
cliffs exposed to the south, so that various atmospheric influences 
have been at work. The sea has had little to do with it, except in 
removing the masses which from time to time fall on the shore. Such 
a mass may be seen on the left of the photograph ; it fell shortly 
before the picture was taken, but has now disappeared (April, 1895). 
The chief effect of the rainfall on these particular cliffs has been 
to carve out the sharp ridges and arretes which are so conspicuous a 
feature in the landscape. Here and there tiny earth-pillars are 
found, with a stone on the top, which has for a brief time arrested 
the washing away of the clay ; elsewhere, miniature ravines or corries 
show where gathering tiny streams have run together and caused a 
temporary waterfall. In the centre of the photograph, however, there 
is a ravine of an entirely different character. It resembles the 
ravines at Filey, and the gaps of Hunmanby and Speeton. It is a 
valley excavated by a perennial stream which rises from a spring on 
the top of the cliff some 150 yards back. There are several valleys 
of a similar character between Sarnwick and the North Landing at 
Flamborough Head. These springs, however, effect little in the way 
of denudation compared with the numerous sipings which trickle 
down the face of the clay cliffs in other sections. The damage they 
do is incalculable, no amount of drainage seems capable of retarding 
