MORTIMER: ORIGIN OF CHALK DALES. 
37 
admit of the clay being- squeezed out and washed away at the S. 
side of the dale ; and here and there masses of chalk left unsup- 
ported would break off and fall on their edges, in the position now 
occupied by these Back Dale mounds. 
Again, on reaching the next dale (Thixendale) we observe, as 
previously mentioned, displaced masses of rock on one side of the 
valley only. The base of the chalk on the north side of the valley 
is from 20 to 50ft. higher than on the south side ; the weight of the 
superincumbent rock, resting on yielding clay, has caused masses of 
chalk along the north side of the dale, to break off and slide to lower 
levels, leaving a ledge or terrace above, and somewhat increasing 
the dip of the beds of these slipped masses. Springs, one at Burdale, 
and one at Thixendale, issue from this side of the dale only. 
From the opposite dip of the beds on the two sides of the 
valley, as shown in the section, you will observe that this dale 
(Thixendale) runs for some distance along an anticlinal, the very 
place where the greatest strain would be, and a fracture most 
liable to occur, and the force has been sufficiently great to 
completely sever the rock here and in Back Dale, and to throw up 
the intervening mass to a height varying from 10 to 50 ft. 
Other important displacements exist in this neighbourhood. 
Near Burdale, about 2 J miles E. of my line of section, at the junction 
of Fairy Dale with Thixendale, there is a well ascertained 
fault ; at the west side of Fairy Dale a fine spring of water issues, 
and the red chalk comes to the surface, w^hile on the same level 
at the opposite side, close to Burdale Station, about 60 yards distant, 
a well was sunk about the year 1867 more than oOft. in depth, 
through somewhat disturbed rock, and it was at the bottom only, 
that red chalk was found. In the autumn of 1880, I obtained with 
the pick and the boring rod, a section (fig. 5,) across the bottom of 
Fairy Dale, at a point about f of a mile from the mouth of the Dale, 
and a little N.E. of " Fairy Stones," which also proved faulting. But 
here the downthrow is only about 8ft. , and what at first seemed a little 
perplexing, is on the W. or opposite side to the downthrow at the mouth 
of the dale. Fortunately the cause of this anomaly is near at hand. 
The Fairy Stones, near to it, previously mentioned, are large 
