1869. ] SEARLES WOOD—BOULDER-CLAY. 103 
such a mounting, in the form of the lower elevations intervening 
between the Cheviots and the Northumberland coast, yet it does 
not appear to me that the conditions of that part of the western 
slope in which Shap Fell lies, offer any indications of such an up- 
ward transit*, or that the position of the dividing ridge generally 
would allow of the possibility of it. 
We have therefore but to fall back upon the explanation of a 
floating-ice transit, permitted by an adequate submergence ; and this 
explanation is strengthened by the absence of these boulders in 
the older or chalky part of the clay, since otherwise they ought to 
be present in this part equally as in the other. 
Mr. Archibald Geikie, in the year 18637, put forth his theory 
that the origin of the Scotch Boulder-clay was due to the extrusion, 
from the sea-foot of an ice-sheet enveloping the land, of the miscel- 
laneous material which such a sheet would in its motion seaward 
have degradedt. This hypothesis is that which for a long time I 
have entertained as the only true one of the origin of the Glacial 
clays of the east of England; and I venture to suggest that the 
application of it to the case now under consideration will not only 
harmonize with all the facts, both paleontological and physical, but 
explain that otherwise inexplicable circumstance, the positions of 
the purple clay without chalk, to which attention has been called. 
In the same outline map I have indicated, by tint shading, that 
area which [ regard as sea during the deposit of all but the earliest 
part of the chalky clay, the unshaded part having been enveloped in 
an ice-sheet, which barred out the sea from all those depressions 
which, being below its level, would otherwise have been occupied 
by it, Just as is the case at the present day along the west coast of 
Greenland according to Arctic voyagers§. The same shading that 
indicates sea indicates also the area over which the chalky clay occurs, 
except that, to curtail its dimensions, the map does not extend south- 
* The whole of the great basin drained by the rivers Lowther and Hden (on 
the side of which Shap Fell lies) is furrowed by a numerous set of small paral- 
lel ridges, with their prominences in roches moutonnées. These all run from 
S.8.E. to N.N.W., and a glance at the beautifully shaded contours of the Ord- 
nance map shows at once, by a cowp d’eil, that a great ice-sheet has moved 
down this basin towards the Solway shore. Similar features are afforded by 
the contour-shading of the slopes on the other (or eastern) side of the dividing 
ridge north-west of Newcastle, where the motion has been similarly outward 
from the dividing ridge, being there from W.S.W. to E.N.E. Mr. T. M‘K. 
Hughes, of the Geological Survey, kindly indicated for me such striations as he 
had observed on the rocks of this neighbourhood ; and they agree generally with 
the ice-motion which the map-contours indicate. 
t Trans. of the Geol. Soc. of Glasgow, vol. i. part 2. 
{ The Rev. J. B. Watson too, in his memoir on the Glacial beds of Arran 
(Trans. Royal Soc. of Edinburgh, vol. xxiii.), adopts the same hypothesis, and 
adds some valuable information as to the causes in operation at the ice-foot of 
the Norway glaciers, derived from personal observation. The Glacial condi- 
tions of the. period of the chalky clay were, however, far in excess of any thing 
now obtaining in Norway, and more analogous to those on the west coast of 
Greenland, and along the skirts of the ice-bound land of the Antarctic con- 
tinent. i 
§ See Dr. Sutherland in Quart. Journ. Geol. Soe. vol. ix. p. 301. 
