1869. | SEARLES WOOD—BOULDER-CLAY. 101 
posited the clay which contains them, in any other way than by 
the occupation by an ice-sheet of the great vale that extends along 
the scarp of the Wold where the red chalk crops out. 
Another important feature bearing upon the relationship of the 
chalky to the chalkless clay, is the absence in the one and the pre- 
sence in the other of boulders of the well-known peculiar granite of 
Shap Fell in Westmoreland. During the several years that I have 
occupied myself in examining and mapping the Glacial beds over 
the east of England, I have never seen such a thing as a fragment 
of this granite either in the various sections examined or among 
the numerous boulders which, exposed by atmospheric agencies, 
have been collected from the fields and placed by the roadside or 
by farmhouses &. Neither Mr. Rome nor myself ever observed one 
along the Holderness coast, where the chalky clay and the purple 
clay with some chalk occupy the cliff; but immediately that we 
passed these limits and entered, about Flamborough Head, upon 
the region of the purple clay without chalk, we found them in 
plenty ; and Mr. Rome informs me that he has seen them along 
the whole coast north of Flamborough, where this purple clay with- 
out chalk alone occurs, as far as the mouth of the Tees; and it is 
to him that [ am indebted for pointing out to me (which he did 
more than two years since) the restriction of these boulders to the 
clay without chalk. 
Although neither he nor myself was able to find any of these 
boulders along the Holderness coast, they are nevertheless said to 
occur as far south as the Humber mouth * ; ; and there is no reason 
to suppose that such may not be the case, though rarely—because 
the chalky clay and the purple clay with chalk are, on this coast, 
capped in two or three places by outliers of the purple clay with- 
out chalk, from which these boulders might be derived. 
In order to render the explanation which I offer of these facts 
intelligible, a small outline map of the north of England (fig. 1, 
p- 102) accompanies this paper, and in it are carefully shaded the 
slopes of the great dividing ridge of the north of England. The 
position of Shap Fell being on the western side of this dividing 
ridge, it is clear that one of two events must have occurred to enable 
its boulders to pass over the higher ground which separates the Shap 
country from the eastern side, over which the purple clay containing 
these boulders is distributed. The one event would be their transit 
by land-ice moving, not as it usually does from higher to lower 
ground, but upwards against the acclivity, and over the dividing 
ridge into the eastern area; the other would be the submergence of 
the country to an extent sufficient to permit the floating over of 
masses of ice freighted with these boulders. 
With respect to the first of these alternatives, although we know 
that ice impelled by the force of the rearward mass of the sheet 
will, when this mass derives sufficient force by a descent from 
elevations considerably higher than the intervening obstacle, rise 
and pass over that obstacle—and though we may find traces of 
* Quart. Journ. Geol. Soc. vol. xxi. p. 44. 
