3^ THE UNDERGROUND WATERS OF NORTH-WEST YORKSHIRE. 
The fault, the change in the character of the rocks, and tlie 
steep undulations of the bedding might be expected to have a 
great effect upon the flow of underground water. 
Assuming that underground channels were established along 
the master-joints, what causes the water to flow out at Aire 
Head? It should be borne in mind that the direction of 
flow of underground water is as much or more determined by 
the ease with which it can get oitt at a particular place as the 
freedom with which it can get in at some other place ; indeed, 
paradoxical as it may seem, the former is much more the cause 
of the latter than vice versa. 
Now in the district south of the fault the rocks are bent 
into an arch and trough, so that the limestone under Cawden 
comes up against the plateau limestone at and about Grey Gill, 
dips under the shales below Malham village, and re-emerges at 
Aire Head ; and here the great springs break out (Plate XI.). 
Again assuming that the Tarn water goes by way of or near 
Grey Gill, w^hat causes it to turn ofl" at so sharp an angle to its 
then course? The answer appears to be (though several reasons 
might be suggested) that Aire Head Springs are situated at or 
within a few yards of the nearest and lowest point of re-emergence 
of the limestone of Cawden as it rises towards Kirkby Top. 
Moreover, the joint systems, which showed such remarkable 
persistence and regularity in the gently inclined limestone of 
the plateau, are inconstant in direction in the more disturbed, 
folded, and perhaps crushed, limestones of the southern area ; 
but determinations made between Scale Gill Mill and Aire 
Head give readings of 
N. 10° W. mag. ^ 
K 60° W. 
N. 35° E. 
K 35° W. 
N. 15° W. 
K 45° E. 
-N. 20° E. 
N. 22° E. 
(Declination 18° W.) 
two sets. 
master-joint. 
