Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/330

 side of the main valley, between Evesham and Tewkesbury, isolated patches of the unstratified qnartzose flinty gravel of the lower series occur on its upper edge, at Green Hill, Evesham, and Mount Pleasant, Pershore, whilst over portions of the main valley itself similar beds are distributed at elevations varying from 103 feet to 67 feet above the river. At the southern base of the same part of the main valley, stratified deposits of " Local Drift" are met with, containing a small percentage of quartzose pebbles, flints, and quartzose sand, as at Beckford, where marine shells and mammalian remains have been found. They appear to extend around a considerable portion of the lower part of Bredon Hill, and may perhaps be considered to form a sort of link serving to connect the unstratified gravel of the lower series of the Avon district with the stratified beds of the Severn valley which contain marine shells and mammalian remains. I have also attempted to show that the freshwater beds of gravel and brick-earth constitute platforms, divided throughout their length by the present river, but capable of being classed as one deposit, which appears to me distinguishable from the adjacent unstratified beds of the lower series.

On reviewing the phenomena presented by the drifts of the Severn valley, we find, for the most part, but little resemblance between them and the superficial deposits of the Avon valley and district. In some localities there are compact beds of loamy gravel, rarely containing marine shells, which somewhat resemble the unstratified drifts of the lower series in the Avon valley. In others we encounter cleanly washed stratified sands and gravels, such as have not been found in any part of the Avon district. The absence of any deposit resembling the freshwater gravels and brick-earths of the Avon valley and some of its tributaries is remarkable, their position with regard to the river being occupied in the Severn valley by beds containing a few traces of marine shells and, occasionally, mammalian remains.

Remarks on the Evidence bearing upon the origin of the Freshwater Gravels of the Avon Valley.

Leaving out of the question any speculative attempts to correlate the drifts of the upper and lower series in the districts of the Avon and Severn, as being premature in the present state of our knowledge of the subject, I propose to confine the following observations to the evidence deducible from the facts already known regarding the probable conditions which gave rise to the accumulation of freshwater gravel in the Avon valley. The supposition, made by Strickland, to explain the occurrence of gravel containing freshwater shells and mammalian remains at Eckington and Defford, and its connexion with the unstratified quartzose flinty gravel at Bredon, is as follows : — " I can offer no other explanation than that formerly proposed, viz. that after the beds of marine gravel had been deposited where we now find them, and had been laid dry by the elevation of the land, a large river, or chain of lakes, extended