362 Rev. Dr. Irinng — An Ancient Eduary. 



true, as far as my observations have gone, that, they are much 

 " broken, worn, and even comminuted : " for one even tolerably 

 perfect shell there are hundreds of fragments of shelly debris, 

 speaking to us eloquently enough of their drifting inland from time 

 to time from the outer marine area. Some of the little Oysters 

 0. flahellula) found for example at Yateley, were so much abraded 

 that it was only after comparing them with many forms in the 

 Jermyn Street Museum (with Mr. Newton's kind help) that I could 

 convince myself of their specific identity. 



The Upper Sands. 



Messrs. Gardner, Keeping, and Monckton, in a recent paper,^ 

 state that "the beds [of the Upper Bagshot], and what can still be 

 recognized of their fauna, are such as might have been formed in. 

 an open sea of considerable depth." But this statement amounts to 

 very little, because, so far as the fauna is concerned, there is nothing 

 inconsistent with the view that the molluscan forms which they 

 have tabulated might just as well have been left by creatures which 

 inhabited a shallow salt-water estuary. This will, I think, be clear 

 to any one who will take the trouble to work through their list with 

 the aid of such a reliable work as Woodward's "Manual of the 

 Mollusca." That they are right in correlating the Upper Sands of 

 the London Basin with the Barton of the Hampshire Basin is very 

 probable ; indeed, my own studies, which have proceeded rather on 

 physical and stratigraphical lines, have led me to the same con- 

 clusion as that at which they have arrived ; namely, that the break 

 postulated at the base of the Upper Sands is in reality very 

 inconsiderable. So far from requiring any great length of time to 

 convert this Eocene delta with its swamps and lagoons into a tidal 

 arm of the sea, we know that such changes may take place without 

 any great draft on the bank of geologic time, seeing that within 

 a 1000 or 1500 years the swamps and lagoons of the Yssel, 

 through which, Tacitus tells us, Germanicus led his forces against 

 the immortal Hermann, have all disappeared beneath the waters of 

 the Zuyder Zee ; while several hundreds of square miles of Holland 

 at the present day are only preserved from permanent submergence 

 by artificial barriers. Of the comparative rapidity of this later 

 subsidence of this Eocene area we have evidence in the strata 

 themselves. It is only by such an encroachment of the sea that 

 we can give a rational account of the Bagshot pebble-beds, which 

 recent researches have established as an important fact of Bagshot 

 stratigraphy. These beds vary in thickness from a few inches to 

 five feet or more. They are composed of well-rolled flint-pebbles 

 derived entirely from the Chalk strata, which must have enclosed 

 this Eocene area of deposition on the south and the north-west. It 

 may be assumed that no rivers, that could have drained this Chalk 

 area in Eocene times, even when all allowance is made for its 

 quondam extension, could have manufactured such vast quantities 

 of rounded pebbles out of angular flint fragments as we find sealed 

 1 See Q.J.G.S. vol. xliv. p. 616, 1888. 



