C— GEOLOGY 77 



Durham. 

 It is generally agreed that the Basement Clay of Holderness finds its 

 equivalent in Durham in the Scandinavian Drift discovered by Dr. C. T. 

 Trechmann in hollows in the Magnesian Limestone near Sunderland. 

 Overlying this deposit is a bed of loess, which was in all probability an 

 interglacial deposit ; it is succeeded by Purple (Cheviot) Boulder Clay. 

 The only record of Older Palaeolithic Man in the district is that of a 

 quartzite implement of Chellian type from below the Purple (Cheviot) 

 Boulder Clay. Correlation based on this one implement of crude work- 

 manship (if it be accepted as an artefact) would be premature. 



Northumberland and the Lake District. 

 Our next problem is the question of the linking-up of the boulder 

 clays of Yorkshire, Durham and Northumberland with those of the 

 Irish Sea area. Recent work of the officers of the Geological Survey, 

 admirable in its detail, has established for the Solway-Eden district 

 three main ice advances and retreats, namely, (i) a Scottish ice-advance, 

 (2) a maximum combined Lake District ice-advance which carried 

 boulder clay eastwards over the Tyne gap and over the Stainmore gap 

 into the Tees valley, and (3) a Scottish re-advance. There also appears 

 to be evidence of a weathered boulder clay earlier than any of these 

 episodes. In his valuable paper on the glaciation of eastern Edenside and 

 the Alston block, Dr. F. M. Trotter has traced an ose-train westwards from 

 Hexham by way of the Tyne gap, and has thus connected the maximum 

 glaciation of the Lake District with that which yielded the coastal Hessle 

 Boulder Clay. Previous to this, ice-sheets which advanced over Stain- 

 more during the onset of the Early Scottish and Lake District glaciations 

 fed the glaciers which helped to form the Purple Boulder Clays of York- 

 shire, replete with boulders of Shap granite, Borrowdale lavas, etc. 

 Drs. Trotter and HoUingworth are therefore inclined to correlate the 

 Upper Purple Boulder Clay with the Early Scottish advance, and the 

 Lower Purple Boulder Clay with the early weathered boulder clay of 

 Silloth, and other places. 



The Irish Sea and Cheshire Basin. 



The main glaciation of the Irish Sea region extended to the coastal 

 areas of North Wales and far into the Cheshire Plain. As is well known, 

 during its retreat-stages at the end of this period, the ice gave rise to 

 the glacial lakes Newport, Buildwas and Lapworth, and caused important 

 diversions of river-drainage in the case of the Severn and other systems. 

 In North Wales a boulder clay from the Irish Sea ice sealed up the mouths 

 of several well-known caves in the Carboniferous Limestone, containing 

 floors of Middle Aurignacian implements. Notable amongst these 

 were Cae-gwyn and Ffynnon Beuno, in Denbighshire. Although for 

 a time some difference of opinion was held as to whether or not the 

 undisturbed boulder clay of the Vale of Clwyd actually sealed up the 

 caves, the consensus of opinion was finally in favour of that view. The 

 Snowdonian and Arenig ice-sheets seem to have been able to prevent 

 the Irish Sea ice from advancing far into the hilly region of North Wales, 



