62 SEVENTH REPORT—1837. 
older rocks of Herefordshire and Wales; and hence, at that period, 
the whole island must have been many hundred feet lower than it is 
at present,—nay, it may have been totally submerged, as the absence 
of erratic gravel on the oolite hills, and on the mountains of Wales 
and Herefordshire, does not necessarily imply that those districts were 
dry land when the gravel was drifted into the midland counties, 
since the erratic pebbles would necessarily be directed towards the 
lowest levels, and districts out of the exact line of the current might 
even be in course of local degradation whilst the extraneous matter 
was hurried past them. The probability that the chalk and oolite 
hills of England were principally, if not entirely, submerged, is 
strengthened by the fact that ramifications from the general mass of 
gravel in Warwickshire extend through the transverse valleys of the 
oolitic range, follow the course of the Thames, and cross considerable 
hills near Oxford and Henley, as shown by Dr. Buckland. As the 
marine shells found in this gravel are chiefly of existing species, a 
very recent epoch must be assigned to its deposition ; and as no traces 
have been left of regular tertiary strata, even in small valleys and 
basins sheltered from the action of the northern current, it seems 
probable that the causes which led to the transport of the gravel were 
comparatively transient. The most reasonable supposition appears to 
be that this transport was connected with the elevation of the land, 
the new red sandstone of central England having been covered up by 
younger deposits, when a process of elevation and of accompanying 
denudation commenced, whereby the upper secondary strata were 
removed, and the new red sandstone exposed to the action of the 
marine currents. And when, by a further rise, England was elevated 
above the sea level, the midland counties would present an undulating 
surface of new red sandstone and other rocks, with scattered patches 
of erratic gravel, the relics of the action of denuding currents. But 
whether the northerly current which has effected such devastation 
was the direct result of elevation of the land, and consequently trans- 
ient and violent, or whether it was similar to ordinary marine currents, 
such as that now flowing through the Pentland Firth, it would be pre- 
mature to speculate. 
These marine detritic deposits consist of gravel, sand, or clay, in va- 
rying proportions. The gravel contains numerous pebbles of white » 
or brown quartz, mixed more or less with other substances. It is 
in general very imperfectly, or not at all stratified, there being some 
local exceptions to the rule. It is believed that no mammiferous re- 
mains occur in this drift, the only genuine fossils being marine shells, 
which have been found in some few localities in Cheshire, Shropshire, 
Staffordshire, and Worcestershire. And it is remarkable that it occurs 
independently of the minor variations of the surface, covering ex- 
tensive tracts, and capping hills of 400 or 500 feet in height. 
There are three principal varieties of marine drift; Ist. erratic 
gravel without chalk flints; 2nd. erratic gravel with chalk flints ; 
and 3rd. local or non-erratie gravel. The gravel without chalk flints 
covers the country to the North and West of the Warwickshire Avon. 
