96 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
in that direction would be completed by currents originating in the 
elevatory movements by which the great central chain, after the 
transport of the blocks across it, was elevated above the surface of 
the ocean. The denudation of the vale of York and the formation 
of the oolitic escarpment of the Wolds would take place subsequently 
during the gradual elevation of that region, in the manner in which 
the German Ocean, or English Channel, is now performing a similar 
work of denudation, and forming similar escarpments along our ex- 
isting coasts. The existence of boulders from the Cumbrian moun- 
tains on the highest parts of the Eastern moors is thus I think simply 
explained, and the third great difficulty of the problem entirely re- 
moved. 
27. It should be observed, that though I have contended against 
the extreme limitation which many geologists have appeared inclined 
to impose on the period of transport of erratic blocks, it is not neces- 
sary to insist on any material extension of that period as essential to 
the explanations of the theory above-given, which admits of as recent 
an epoch of erratic boulders as any theory which assumes their sub- 
aqueous transport. 
The transport of boulders in the other directions in which they are 
found, and the spreading of an extensive layer of smaller detritus over 
the surrounding plains, would be the necessary consequences of the 
great waves above described. It is unnecessary to enter into any 
details respecting these phenomena: it only remains, in order to 
complete the view now given of the denudation of this district, to ex- 
plain the manner in which I conceive its great diverging valleys to 
have been formed. 
28. Formation of the Valleys.—Let the followmg diagram repre- 
sent an elevated range with the valley A BC D deeply cut into it, by 
the agency of water during the gradual emergence of the range from 
beneath the surface of the ocean. The dotted line C 6d...D re- 
presents a section of the bottom of the valley by a vertical plane and 
Cac...¥F a section by the same plane of what would have been the 
surface of the elevation if there had been no denudation. a, 6, ¢, d, &e. 
c 
Fig. 13. a 
eft MUMUn 
GEEZ Yiiflon Z 
Y= ry gai 
<M FN de 
Hae as a 
F Se SEES Slee ee ae - mmm Y 7 WL - 
WW ccm ar 
ee ee ln 
: MM MU 0 == 
le Mb LL me me ee EE 
Go “ 
D 
are horizontal lines indicating the positions of the surface of the ocean 
with respect to the elevated mass, at different epochs during its eleva- 
tion. Let us also suppose a dislocation to have passed along the line 
of the valley, se 
Previously to the surface of the ocean occupying the position a 6, 
all the portions of the mass above that plane, and between the actual 
surface and the imaginary one C F, would be denuded, and the upper 
