part 3] I.Uss. ESTC. OF THE DTJBHAU (OAST. 1 s ( .) 



can also be adduced, pointing to the possibility of a prolonged 

 Interglacial interval after the retreat of the Scandinavian ice- 

 sheet . 



(a) Evidence from the marine shelly faunas in the glacial beds. 



(b) Possible Interglacial fluviatile erosion between the retreat of the 



Scandinavian ice and the oncoming of the local glaciation. 



('M — Various gravelly knolls and kaims left on the retreat of 

 the latest Cheviot ice-sheet in the Durham coastal area, contain 

 fairly abundant small wa,terworn fragments of marine shells, doubt- 

 less the scrapings of an old shore-line. They arc especially 

 abundant in a gravel-pit near the summit of one of the Sheraton 

 kaims, 3^ miles inland from the eoast, at an altitude of 500 feet 

 4i hove sea -level. 



On the assumption that there had only been one glaciation, it is 

 difficult to understand how the latest movement of the ice travelling 

 in a southward direction eould include the material of a shore-line 

 which presumably would have been already covered by ice or 

 obliterated by the previous ice-sheets. 1 have for some time 

 collected the shelly fragments from these kaim gravels, and find 

 the series of mollusca to be of a decidedly less arctic character than 

 those which occur in the much older Scandinavian Boulder-Clay at 

 Warren-House Gill. An enumeration of the mollusca from these 

 deposits is given on p. 194. 



The Scandinavian Drift contains such thoroughly Arctic species 

 as Cardium islandicum Linnaeus, 0. grcenlandicum Chemnitz, and 

 the curious shell Cyrtodaria siliqua Spengler (now confined to 

 Arctic America), forms apparently wanting in the later kaims. 

 The latter contain, in fact, a fauna much more closely resembling 

 that of the North Sea of the present day, with numerous in- 

 dividuals of Tellina halthica Linnaeus and Twrritella. Both 

 deposits are unfortunately rather scanty in species, the kaims 

 especially so, but the difference in the faunas, both evidently 

 derived from the North Sea, is sufficiently striking. 



It might, of course, be argued that the difference is due to 

 difference of depth, and that the Scandinavian ice travelling across 

 the North Sea tore up the mud containing the shells from fairly 

 dec]» water, while the Cheviot ice skirting the shore-line contained 

 a littoral fauna. 



Mr. (J. W. Lamplugh recently told me that he found that in 

 York-hire the shells of the Middle Gravels are generally less Arctic 

 than those in the Basement-Clay, but he considered that this 

 implied that the Boulder-Clay shells had travelled some distance 

 from the cold sea-bed, and that the gravels and their fossils were 

 derived from the working-up of shore-deposits. 



These facts agree with my observations of the Drifts of the 

 Durham coast ; but 1 am inclined to believe that the shells of the 

 latest kaims represent the scrapings of an Interglacial and not of a 

 Preglacial shore-line, with a fauna more closely approaching the 

 present one. 



