362 
HUGHES : IXGLEBOROUGH. 
But if the movements have been of much less intensity and 
shorter duration, if the old sea bottom with the deposits of ages 
heaped up over it has not been upheaved above sea level over 
the whole area, but yet changes affecting the currents and the 
forms of life have been setting in, so that a different sediment 
is carried over the area, and conditions become unsuitable for 
inost of the old forms of life, and readjustments of shore lines 
and of depths have encouraged new forms to migrate into the 
area, then it is often difficult to draw a line exactly showing 
where the new order of things commenced. The newer and 
older beds are, at am^ rate as far as can be seen within small 
distances, parallel. If great deposits of as yet unconsolidated 
mud or sand are being Avasted awa}^, the resorted material is 
mud or sand, and there will be little difference betw^een the new 
deposit and that on which it rested. Yet even when such uni- 
form and gentle movements are taking place over one area, if 
there is evidence that changes of such a character as to introduce 
a new facies have taken place, we ma,y be prett}^ sure that the 
movements have not been quite uniform, and that denudation 
has every here and there been exposing new^ rocks which in time 
get buried up, and thus fragments of the harder parts are drifted 
over the old surface, and occur either sporadically or in small 
banks of gravel, which form lenticular beds along the base of 
the new series. 
We have on Ingle borough excellent examples of both these 
conditions. The conspicuous unconformity at the base of the 
Carboniferous rocks of which I shall have to speak more in detail 
by and by, is an example of enormous lapse of time, of tremendous 
uplifting, folding, and denudation of the older rocks before the 
basement bed of the newer was laid down upon them. It rarely 
rests on the same stratum of the underlying series for more than a 
few feet. But in the case of the basement bed of the Silurian, 
we have an example of the second kind. It is difficult to find, 
difficult to trace when found, and rests generally upon a bed 
in the older series, which, with small variations in thickness and 
lithological details, evidently represented approximately the same 
horizon at the top of the Bala Beds, and it succeeds well-known 
beds of that formation which can be correlated over wdde areas. 
