secretary's r eport. 
177 
It was seen tliat in the open passages in the neighbour- 
hood of Alum Pot was an opportunity for putting this theory to 
the practical test by following the water step by step in its 
underground journey ings. 
With this object in view your Committee undertook to 
make a survey of some of the more readily accessible channels 
with the following results. 
A plan of the series of passages communicating with Long 
Churn and joining that opening with Alum Pot was constructed, 
and this will be published in due course by the Yorkshire 
Geological and Polytechnic Society. 
On this plan the directions of the principal lines of jointing 
have been marked for purposes of comparison with the direction 
of the caverns. 
It may be confidently said that there is a general parallelism 
between joints and passages, but this is by no means so close 
as was at first expected. 
To account for the want of parallelism between joints and 
passages it is necessary to study the evolution of one of these 
underground chambers. 
The joints in the limestone undoubtedly give the initial 
direction to the underground stream ; but as soon as a channel 
is formed sufficiently large to allow of a free flow of water, as 
opposed to mere soak age, a number of other forces come into play 
which tend to modify the direction so as to cause it to diverge 
somewhat from its original one of strict parallelism to the joints. 
For example, the dip of the rocks causes the erosion of 
the channel to be more severe on one side than the other — 
namely, on the low or " down dip " side — and where there are 
cross- joints the dip may tend to produce a lateral escape along 
one of these so as to give rise to a zig-zag course. 
Up to a certain point the erosion in these underground 
river channels is entirely by solution, but so soon as the ex- 
ternal opening becomes sufficiently large to admit sand gravel 
and boulders excavation by means of attrition comes into 
play. 
