77 
the circumjacent denudation of the limestone may have com- 
menced immediately after the fall of the boulders. The 
absence of boulder-clay may be readily explained by the 
inability of submarine currents to transport it in an easterly 
direction across deep valleys and steep ridges, and finally up 
the steep and (in many places) overhanging face of the 
Keglwyseg cliffs. 
6. Boulders on Limestone Rock-surfaces near Clapham, 
Yorkshire.—After walking about a mile and a half along 
Thwaite-lane, east of Clapham, and crossing one or more walls 
in a northerly direction, one arrives at the base of a steep 
limestone escarpment. On rounding the east end of this 
- escarpment, and walking up a stone-covered slope on the left, 
the lower part of the great limestone plateau marked Norber 
on the Ordnance maps suddenly comes into sight. It cannot 
fail to be noticed that the surfaces of the limestone rocks are 
often flat, and terminate in miniature cliffs with steep brinks, 
as if whole blocks or fragments of rock had been removed by 
land ice, floating ice, or, according to Professor Phillips, by 
powerful currents. Partly resting on fragmentary rocks, and 
partly on flat and extensive rock surfaces of a lhght grey 
colour, there is what may appropriately be called a grim array 
of many hundreds of huge and black Silurian grit and slate 
boulders, which are apt to suggest the idea that they are 
about to spring into life! I think it must be obvious to any 
one who has made the pedestals of boulders a special study 
that many, if not most, of these boulders have found resting- 
places on pre-existing fragmentary projections of limestone 
rock, after the manner of the perched blocks which may be 
seen in all countries which have undergone extensive glaciation, 
and | have little doubt that, had Mr. Tiddeman’s attention* 
been particularly directed to the subject, he would have agreed 
with me that the formation of the pedestals must have partly, 
if not chiefly, taken place before the boulders were left on 
them by the melting of the ice which transported them. But 
Mr. Tiddeman’s object was the more important one of dis- 
covering glacial striz on the pedestals under the boulders 
where they had been protected by the boulders from the 
action of rain. 
7. Hvidences of the Pre-existence of many of the Pedestals. 
—That many of the pedestals must have existed before the 
arrival of the boulders would appear from the following 
facts :—1. Many of the boulders have no pedestals, and many 
* See Quart. Journ. Geol. Soc., vol. xxviii. 
