145 
level, and Mr. Yarley informed me that he found them on 
the other side of the moor, facing the Wharfe valley, at 
about the same height. 
Remarks on the Origin of Escarpments. — We do not 
stand in absolute need of the occurrence of erratic blocks as a 
proof that the moors of north-west Yorkshire were once under 
an ice-laden sea. The amount of decomposed shale and the 
number of stones and boulders entering into the composition 
of the drift-deposits can only be explained by supposing that 
a corresponding amount of denudation, as we have seen, must 
have mainly taken place on sea-coasts. The sea could not 
have abstracted the shales from the hill-sides without leaving 
indentations and ujidermining the overlying harder strata, so 
as to leave steep escarpments and cliffs. At a stationary 
level, the terraces would be rendered more or less horizontal, 
but as the land gradually moved up and down the sea would 
follow the outcrops of the shales so as to leave inclined or 
irregular terraces. The shales would often be left forming 
the platforms, or lower parts of the superjacent escarp- 
ments, but the sea would likewise, where its action was 
sufficiently persistent, wear out a terrace in the more solid 
rocks, and accordingly we often find terraces with both 
platforms and cliffs consisting of hard rock — for instance, on 
the south-west and west side of Embsay Moor, on the 
Hombald's Moor side of the valley between Skipton and 
Bolton, on the western side of Brimham Moor, &c., &c., 
(see plate). Many of the platforms of the terraces of the 
West Riding are covered with drift containing rounded 
among angular stones, generally local, but sometimes 
erratic (on the north side of . Harden Moor, both sides 
of Rombald's Moor, and in innumerable other instances). 
This drift exactly corresponds with what one might sup- 
pose to have been deposited on a sea-beach, with a steep 
declivity below, under mixed glacial and marine condi- 
