34 
MOETlMEPi : OEIGIN OF CHALK DALES. 
short distance at its termination, where it rises upwards through 
the chalk. Throughout the greater length of this valley the beds of 
chalk on each side are found in nearly ever}^ pit to dip more or less 
from the centre of the valley, or in opposite directions, while the 
base of the chalk is highest on the north side. For a considerable 
distance along the north side of this dale, extending from Raisthorpe 
to within half-a-mile of Aldro, large masses of the chalk hillside 
have slipped to lower levels, and formed a kind of broken terrace 
or ledge. On the opposite or south side no well-marked slip is 
noticeable. 
Proceeding along the line of section into Back Dale, the beds 
of the intervening ridge are found at first to dip 5° north and 
diminish to 2^ north near the centre of the ridge. At the foot of 
the southern hillside of Back Dale, the bottom of which is in the 
main only a few feet in width, there is about half-way up the valley 
a line of remarkably formed mounds extending for about half-a-mile. 
The section cuts them. 
During the second week in October, 1879, in the presence of 
Mr. Dakyns, of the Geological Survey, and Dr. Wood, of Driffield, I 
caused three excavations to be cut across the ridge of the most 
western mound, and at a depth of one to two feet, the hard chalk 
rock was reached, the beds of which were found standing at an 
angle of 35° N. in the most westerly cut, and at an angle of 65° N. 
in the cut near the summit of the mound. These excavations showed 
that the masses of the chalk had slipped from the adjoining hillside 
and fallen on their edges. No trace of any similar slipped masses is 
observable on the opposite hillside. These slips are the most striking 
of their kind that I know of in the Wolds ; though slips of a 
like kind are found all along the outer margin of the chalk wolds. 
The above mentioned are exceeded in distinctness of form only by a 
line of hillock-formed masses extetiding from near Tliorp-Bassett 
towards Wintringham, and called " Stack Hills." Our line of section 
continuing over the broad and somewhat unevenly topped high ground 
on the N.N.E. side of Back Dale presently cuts a chain of very 
curious hollows in the surface, five in number, rudely linked together 
at their ends, which seem to branch from a little dale, which runs 
