508 MESSES. A.BNOLD-BEMEOSE AND DEELEY ON [Aug. 1 896,. 



the view. Nor could it have existed when the high-level gravel on 

 the northern escarpment of the Trent, shown in section (fig. 3,. 

 p. 502), was being deposited ; indeed, it has clearly been excavated 

 at a comparatively recent date, and was once a shallow lake, which 

 has since been drained by the deepening of the Trent Yalley. It 

 seems to have been formed by a glacier at the same time as the 

 'trail,' or, which is much less likely, by the removal of a 

 soluble bed in the Keuper Marl below. 



We are now in a position to discuss the age of the bone-bearing: 

 deposits. 



Although in no case have we found any of the high-level gravels 

 resting upon either the Pennine or the Chalky Boulder Clay, from 

 the positions which the gravels occupy on the sides of the valleys 

 and the presence in them of flint from the Boulder Clays, it may be 

 safely concluded that all the river-gravels were deposited at a sub- 

 sequent date. It only remains, therefore, to show how they are 

 related to the gravels, etc., of the lower plain, and to decide whether, 

 they are of Interglacial or post-Glacial age. 



It is generally conceded that glaciers have never reached those 

 portions of England that lie to the south of the Thames Basin.. 

 There we have no true boulder-clays. But even thus far south 

 deposits are to be found which it is difficult to account for, except on 

 the supposition that the climate was at one time very cold. When 

 such surface-deposits were being formed, other portions of England 

 were being glaciated, and, therefore, such deposits belong to a 

 British Glacial Period. Any period of cold which was sufficiently 

 severe to cause glaciers to appear in Britain we may call a ' glacial 

 period,' and any period intermediate between the two glacial periods 

 an 'interglacial period.' Whether it is wise or the contrary to- 

 retain a classification connoting a physical change in the condi- 

 tions under which the deposits were formed is open to argument, 

 but such considerations need not influence us in settling the relative; 

 ages of the particular deposits with which we are dealing. Conse- 

 quently, whether the 'underplight' and trail be due to an agent 

 owing its existence to a change of climate, or to some other cause,. 

 we may with confidence assert that they are now being denuded 

 from most if not all the areas in this country on which they were 

 at one time formed, and are typical of a particular epoch or epochs 

 of the Pleistocene Period. 



Just as it has been suggested that the formation of certain rubbly 

 deposits, etc., which have been formed in the South of England must 

 be attributed to the action of frost, heavy masses of ice or snow and 

 of floods on a frozen ground, so I would attribute the formation of 

 similar deposits in the Midlands to similar agencies. But some of 

 the surface-phenomena presented by the gravels, etc., which have 

 been described above can, I think, only be explained on the as- 

 sumption that, at a comparatively recent period, and after the rivers- 

 had excavated their valleys to a depth of within 15 or 20 feet 

 of their present levels, an ice-lobe from the basin of the Irish Sea» 



