A. J. Jukes-Bi'owne — Interglacial Land-surfaces. 149 



In discussing questions of relative age, therefore, it would be 

 much better to use the terms Older and Newer Pleistocene instead of 

 Glacial and Post-Glacial, the true test of age being the constitution 

 of the Mammalian fauna, and not the cessation of glacial conditions. 

 I can see no reason why the newer Pleistocene fauna should not 

 have occupied our southern and midland counties before the forma- 

 tion of the later glacial deposits of Cheshire and North Wales, 

 provided only there was a time when a land-surface existed that 

 was sufBcientljr free from snow and ice to permit of their immi- 

 gration. If this were the case, Man was probably a contemporary 

 immigrant ; but this would not make him Pre-Glacial : consequently 

 it is needless to compare the fauna of the Welsh caves with that 

 of the Pre-Glacial Forest Bed. 



The question then is, do the facts, so far as we know them, afford 

 any evidence in favour of the supposition that there was a land- 

 surface free of ice anterior to the submergence during which the 

 later glacial deposits were formed ? I think this question may 

 certainly be answered in the affirmative ; it is indeed a remarkable 

 coincidence that three separate inquirers, each studying a separate 

 district lying between the same parallels of latitude, should have 

 independently arrived at conclusions which favour the above sup- 

 position. These three districts are (1) Lincolnshire, (2) South 

 Derby and Nottingham, (3) North Wales. 



One of the most striking points in the Pleistocene Geology of 

 Lincolnshire is the conti-ast and distinction between the two great 

 groups of glacial deposits ; on this point I agree with the late 

 Searles Wood, Jan., that the facts indicate the lapse of a very 

 considerable interval between the formation of the older and newer 

 deposits. Whether the older Boulder-clay was formed on land 

 or beneath the sea is of course an open question, though I incline 

 to the latter opinion ; but it certainly seems to have been exposed 

 to extensive erosion before the deposition of the newer red and 

 brown clays. The facts favour the idea that a land-surface existed 

 which was free of ice, but exposed to the action of rain and running 

 streams, and that the district remained above water long enough for 

 a distinct valley-system to be produced. Submergence then took 

 place, the ice-laden waves of the North Sea attacked the coast-line 

 and cut it back for many miles, forming a plane of erosion which 

 terminated in a line of cliffs. More rapid submergence ensued, the 

 cliffs and the wolds sank beneath the sea, and the valleys were 

 filled up with gravels and Boulder-clays, which bear evidence 

 of their marine origin in the shells which are found in them up to 

 heights of 200 feet.^ Here, therefore, we seem to have fairly good 

 evidence of an inter-glacial land-surface. 



Again, the Pleistocene deposits of South Nottingham and Derby 

 have recently been described by Mr. E. M. Deeley, who divides the 

 series into Older, Middle and Upper, assigning the East Anglian 

 Chalky Boulder-clay to the Middle stage ; from his description 



^ See Quart. Journ. Geol. Soc. vol. xli. p. 130, and " The Geology of East 

 Lincolnshire," Mem. Geol. Survey, 1887, p. 91. 



