220 
shire shore of the Humber, the Lower Lias is covered up by a 
gravelly accumulation of its own debris, containing numerous 
worn specimens of Grj^ph^ea incurva ; these gravels are evi- 
dently entirely of local origin. By what means the materials 
of the Heck gravel were transported to their present position 
I cannot form an opinion, but they have evidently been 
arranged by water during a period of great depression of the 
surface. It seems at first sight a plausible conjecture 
that they are the result of the action of water upon the 
Boulder Clay ; the stones and sand being deposited on the 
spot, and the clay carried away in suspension to form the 
Laminated Clay, of which I shall have to speak. Against 
this, however, is the absence of boulders of Carboniferous 
Limestone, so abundant in the Boulder Clay in the nearest 
spot at which it is seen: at any rate, if the materials of this 
gravel have been brought by ice, they must have come from 
the west or south-west, not as at Escrick and York from the 
north-west. I find an interesting confirmation of this 
inference at Holme-on-Spalding-Moor. At this place, as I 
ha^e mentioned, the Keuper rises into a picturesque little hill, 
150 feet in height, steep on three sides, but somewhat shelving 
to the south. The summit of the hill is capped with gravel 
about 10 feet thick, very similar to that at Heck, with no 
fragments of the local rock ; on the slopes of the hill the 
red and green Marls are exposed, only covered with a few 
scattered pebbles ; but on the east side a low gravell}^ ridge 
stretches away nearly half a mile from the hill, the gravel 
being composed in great part of flat water- worn fragments of 
green marly sandstone deri\ed from the Keuper. Here, as 
in the neighbourhood of Heck, we find fragments of the 
local rocks only at the lower levels, and we find them only on 
the side of the hill sheltered from a current from the west.* 
* Since this paper was written I have visited some sections near Brough. 
In some gravel pits, near the Cave Eoad, we see a gravel composed of angular 
