TRANSACTIONS OF THE SECTIONS. 63 
_ The gravel with flints occurs chiefly between that river and the foot of 
_ the oolite hills. The chalk flints indicate an easterly current. The 
_ gravel without flints came from the North; but as no section has yet 
_ Shown a superposition of one of these beds of gravel on the other, so 
as to prove a different epoch of formation, they must at present be 
ascribed to one, and the difference of direction in the currents attri- 
_ buted to the obstacles they encountered in their passage ; for instance, 
a current flowing to the S. or S.E. through the counties of Notting- 
_ ham, Leicester, and Northampton, would, on encountering the chalk 
_ hills of Huntingdonshire, be turned to the westward, and carry chalk 
flints into Warwickshire, mixing them with the quartz and other 
_ northern pebbles, whilst the western part of the same current would 
_ flow uninterruptedly through Staffordshire and North Warwickshire, 
depositing pebbles of northern origin in its way, and finally make 
its exit into the Bristol Channel. . The third variety, called local drift, 
as being derived from rocks of its immediate vicinity, occurs in patches 
along the base of the oolite escarpment in Warwickshire, Worcester- 
shire, and Gloucestershire. And as the evidence of superposition is 
here also wanting, the local and erratic drift cannot be ascribed to 
different epochs, but must be assumed as modifications in the effects 
_ of the same great cause; for it is very possible to conceive that whilst 
_ pebbles from a great distance were moving along the central and 
lower parts, local shingle beaches might have been forming (composed 
entirely of the rocks there suffering degradation) at points more out of 
_ the line and influence of the current, just as is the case in rivers, the 
margins of which are often skirted by the detritus of its banks, whilst 
their beds are occupied by pebbles washed from a distance. The 
local drift of Siluria has been shown by Mr. Murchison to be overlaid 
by the northern or erratic drift near Shewsbury, and is therefore re- 
ferred by him to an antecedent epoch. 
The marine drift seems to have been deposited when a large portion 
of England was under water; the next class, or fluviatile, when 
much of it had become dry land. In materials the mavine and fluvia- 
tile are the same, and are hence easily confounded together; but they 
occupy different positions, and contain different organic remains. The 
fluviatile drifts bear a constant relation to the present form of the 
surface, and are commonly found flanking the sides, or covering the 
bottoms of valleys, often at a definite elevation above the present 
drainage: in general they are in a finer state of lamination, which 
proves a more tranquil deposition. They contain mammalian re- 
mains, and freshwater shells of existing species are sometimes found 
with bones of extinct land animals; indeed it is probable that such 
shells will be found to be generally diffused through them. On the 
Warwickshire Avon, platforms of gravel, containing bones and fresh- 
_ water shells, may be traced at intervals down the valley, from Rugby 
_ to Tewkesbury, at heights from 10 to 50 feet above the present 
_ stream; and these platforms are strongly contrasted with the marine 
_ drift which caps the hills flanking the river, both as respects the 
mineral character of the gravel, and the absence of stratification and 
