o 
upper red sandstone.”* I think that most probably the 
former supposition is the true one,. and that these pits are 
caused by the washing away of the red mar-1 and gypsum by 
subterranean streams connected with the river. For the 
gypsum beds occur both here and at Bishop Monckton, where 
another pit has been formed. In the section exposed on the 
right bank of the TTre, the gypsum beds are very much 
contorted, and if this be a general condition of these beds in 
this district,! it is easy to see how readily their substance 
would be removed by the continual waste of running water, 
so as to leave at every place where these subterranean streams 
occur, dome-shaped caverns in the magnesian limestone, the 
uppermost beds of which, I think, overlie these gypsum beds. 
It is worthy of notice that these pits seldom occur singly ; 
but generally they are found in groups of two, three, or four. 
This grouping seems to be due to two or more neighbouring 
folds of the strata which one after the other have been 
hollowed out ; for when the subterranean stream has spent 
its strength upon one contortion, and brought down into the 
hollow which it has made the overlying rock, it will naturally 
attack with greater effect the neighbouring contortion, rather 
than the harder rock of the new red Sandstone, which has 
taken the place of the first. 
Besides the two pits which I have mentioned, several 
others have been formed in the memory of persons now 
living. At Sharrow, one fell in during the night, about 
twenty years ago, and alarmed the inhabitants of a neigh- 
bouring house, who found in the morning little more than the 
breadth of the road between themselves and the pit. About 
forty years ago, some men at Bishop Monckton were making 
* Geol. Trans 2nd series, vol. iii., p. 110. 
+ The upper beds of this series near Ferrybridge are contorted. See Geol . 
Trans., p. 101. 
