MORTIMER: SECTIONS OF DRIFT. 
375 
The peculiar dovetailing of the chalk-gravel with the clays, and 
the clays with the gravel, observed in these sections, is mainly con- 
fined to a limited zone along the inner edge of the chalk range, 
from the sea to the Humber. It is well snown on the coast between 
Bridlington and Danes Dike ; and has formed the subject of inter- 
esting papers by Mr. Dakyns, of the Geological Survey, and Mr. 
Lam plough, of Bridlington.* The eastward extension of the 
dovetailing of the chalk -gravel with the clays appears to be, as far 
as can be observed on the surface, due to a string or chain of sand, 
gravel, and clay ridges and mounds. These ridges are mostly 
arranged with their longest axes parallel with the inner edge of the 
chalk hills, and often merge, or nearly so into one another at their 
base, forming a barrier-ridge at a distance varying from about one 
mile near Bridlington, to nearly five miles opposite Hull, from the 
inner edge of the chalk wolds ; thus preventing to a great extent, the 
eastward flow of gravel-loaded bergs from the eastern edge of the 
land ice, capping the chalk hills. 
The Poundsworth ridge in the neighbourhood of Driffield, con- 
sists of 12 ft. of brown boulder clay, under which is 24 ft. of 
finely laminated marl clay running towards the bottom into clay 
marl and resting on chalk. These mounds are not moraines, but 
seem to have been in the main conveyed by masses of floating ice, 
broken probably from an ice-sheet traversing the North Sea, and 
loaded in part with Scandinavian and Danish rocks. 
Embedded in the beach near Easington, there is a large mass 
of chalk, with its bedding and lines of black flint, unbroken and 
dipping slightly to the east. I am certain it is not part of the 
Yorkshire chalk by the character of its flint ; but as far as I can 
judge it is identical with that of Denmark. Also. in the southern 
portion of the cliffs, between Hornsea and Spurn, foreign flints 
seem to preponderate. A. little north of Hornsea the clays 
contain a large proportion of Yorkshire chalk flint, and bits of red 
* Proceedings of the Yorks. Geol. and Polytc. Society, vol. vii, pages 242 
and 246. 
