28 THE UNDERGROUND AVATERS OF NORTH-WEST YORKSHIRE. 
This observation lent some significance to the fact that a line 
similarly drawn (parallel to the one from Smelt Mill to Cove) 
from Malham Tarn Water Sinks (Plate V.) in a south-easterly 
direction struck the edge of the plateau just where it is breached 
by a ravine, Grey Gill. Grey Gill thus bears the same topo- 
graphical relation to the Tarn Sinks that Malham Cove does to 
Smelt Mill Sink ; but with the difference, suggestive in view of 
the fact that the Tarn Sinks feed Aire Head Springs, that 
Grey Gill Gorge is dry. 
The view thus arrived at inductively seemed sufficiently 
plausible to encourage w^ork by the Geological Sub-Committee, and 
an examination of the district was undertaken by Messrs. J. H. 
Howarth, F.G.S., P. F. Kendall, F.G.S., and W. Simpson, F.G.S., 
with assistance from Mr. Herbert B. Muff. 
For the purpose of and prior to this investigation the 
section illustrating this report (Plate XII.) was drawn by 
Mr. Kendall, and the subsequent examination of the district 
disclosed a series of facts supporting in a remarkable way, without 
completely proving, the assumed analogy between the relations 
of the sinks and gorges in the two cases. 
At the very outset of the inquiry it w^as found that the 
speculations regarding the directions of the master-joints on 
the plateau were thoroughly in accordance with the facts. 
Local discrepancies occurred here and there, especially in close 
proximity to the North Craven Fault, but in general the master- 
joints showed a quite inconsiderable variation from a direction 
160° magnetic (or 142° true), which is 7° to S. of true S.E. 
This direction is indicated on the map accompanying this report 
by the two strong lines to the west of the w^ords "Malham Lings." 
Mr. Bingley's photographs (PI. VI.) show a portion of the 
limestone surface known as Broad Scar between the Tarn Water 
Sinks and Grey Gill. The first is looking tow^ards the water 
sinks, which lie under the curve of the moorland in a line with 
Low Trenhouse farmstead. The second is looking towards Grey 
Gill. On these scars, as is so admirably shown in the photo- 
graphs, the master-joints are very strongly developed and their 
