436 CO. T. Clough—The Whin Sill of Teesdule. 
Going up the northern slope of Noon Hill, in Yorkshire, we have 
a section something as below, beginning from the bottom :— 
a. Limestone, 100ft. (seen, there is probably more covered up by Dritt, etc.) 
6. Sandstone, 50it. 
e. Limestone, 20ft. 
d. Sandstone, 8tt. 
Whin. 
If, from the top of the hill, we walk along the fell ina westerly 
direction for a few hundred yards, we find a great change. We can 
trace the thick sandstone running on, and we can see the limestone, 
c, coming on above it at the next elevation, but when we look for 
the thick limestone, a, we can find no trace of it—instead of the 
limestone we have a bed of Whin, with a thickness of probably 
200ft. at least. This great mass of Whin has suddenly come in, in 
the space between us and Noon Hill, and yet the sandstone shows 
no evident signs of disturbance. anette 
There are many irregularities in the Whin about Birkdale, in 
Westmoreland, and several cases where a Whin bed suddenly ceases 
entirely. In such cases we can often see the swallow holes, marking 
the tops of the limestones, going on in even lines, in spite of all the 
changes in the Whin below. 
The above places may be taken as fairly representing what usually 
occurs in Teesdale when the Whin surface is irregular. I do 
not wish to go beyond the facts at all, nor to give any one the idea 
that there are no instances of mechanical disturbance in the Dale. 
There are probably such instances at the White Force, and at Skue 
Trods, both on the east side of Cronkley Fell, and Sedgwick mentions 
two (op. cit.) on the left banks of the Lune, near Lonton. But, in 
spite of these exceptions, I may safely say that the absence of 
mechanical disturbance is most striking. Of this I think we have 
corroborative evidence in the fact that there are no faults, or veins, 
known in the Dale, that do not go through the Whin equally with 
the sedimentary beds; all the ruptures known have been made sub- 
sequently to the formation of the Whin, there are none contempor- 
aneous with it and made by it; in spite of all its irregularities, in 
thickness and position, it is not known to have once succeeded in 
actually breaking the beds among which it was thrust. 
What does this general absence of disturbance mean? Suppose 
we get a horizontal bed of limestone or of sandstone gradually cut 
through by an inclined face of Whin. The question naturally arises, 
what has become of the bed, where it ends abruptly against the 
Whin face. It cannot have been compressed into nothing. It may 
have been broken up into fragments which have been carried away 
to a distance, and left as isolated pieces in the Whin, or it may be 
lying at the other surface of the Whin, or it may have been dissolved 
up by the Whin. As far as regards Teesdale I do not think the 
first supposition is at all a probable explanation of the facts, for I 
have not noticed any isolated fragments in the Whin; there may 
still, of course, be some, but those there are must be rare, whereas - 
the explanation would require them to be numerous. There are 
