The Geology around Oxford. 321 



rhinoceros, hippopotamus, and other mammalia, together with a good 

 number of hmd and fresh-water shells of existing species, and flint 

 implements regarded as early Palaeolithic. 



It is upon the second of these terraces that Oxford and most of the 

 villages of the Upper Thames valley are built. These gravels are 

 occasionally cemented by iron-oxide into a rock hard enough to be 

 used for a building-stone. It is in this terrace that important finds of 

 the large Pleistocene mammalia have been made. The changes in the 

 courses of the rivers since the epoch of the second terrace have not 

 been very great, the most important being in the case of the Cherwell. 

 The third terrace has also yielded Palgeolithic implements and 

 mammalian remains. Eleven species of fluviatile shells have been 

 obtained from the sand included in one of the gravel beds. There is 

 also a peat bed, where about two-thirds of the mosses, as well as the 

 flowering plants, are still found living in the neighbourhood ; some of 

 the others are Arctic or Alpine. 



The gravels hitherto described may be classed as the low-level group, 

 but between them and the Fourth Terrace there occurred a marked epoch 

 of erosion, during which the Thames cut down its valley to the extent 

 of about 50 feet. It has already been stated that no fossils have been 

 found in this terrace, and the same rule applies to the Plateau-gravel, 

 which M.V. Pocock describes as the Northern Drift. It will be readily 

 understood that mere fragments of this once extensive formation 

 remain, capping portions of the higher grounds, where its presence is 

 indicated on the map by the usual pink colour. It is thought that 

 this drift has an eastern as well as a northern source, but the subject 

 is a too extensive one to be dealt with in a local notice. We must leave 

 the Plateau- gravel and the development of river valleys for the present, 

 merely remarking that, according to Prestwich, since the beginning of 

 the Pleistocene period, when the so-called ' Westleton Beds ' were 

 formed, there has been erosion of the valleys to a depth of 450 feet, 

 the greater part of which was accomplished in Glacial times. Maps 

 showing denudation of valleys since the formation of the High 

 Terrace, and since the epoch of the Wolvercot Terrace, are supplied in 

 the text. There can be no doubt that speculative physiography is 

 a very popular branch of geology, and one which has come to the front 

 enormously of late years. Mr. Harmer's paper on "Lake Oxford and 

 the Goring Gap " is a testimony to the interest which the subject has 

 evoked. 



The question of water supply is dealt with in the latter part of the 

 memoir. The original supply of water to Oxford was obtained from 

 wells sunk in the Yalley- gravel. There are also numerous springs 

 which are thrown out where the water in the various sands, principally 

 of Jurassic age, is held up by the underlying clays. Hence the supply 

 of surface water may be deemed fairly adequate, and it is fortunate 

 that this is the case, since artesian boring in the valley of the Upper 

 Thames cannot be regarded as a success. This is due to the salinity 

 of water from strata below the Great Oolite, which is not as yet satis- 

 factorily explained ; but it will be remembered that even the Forest 

 Marble in the Swindon deep well yielded a water almost as saline as 

 that of the sea. "We fully concur in the remarks of Mr. Fisher that 



DECADE T. VOL. Y. NO. YII. 21 



