C— GEOLOGY 87 



Hill (350-400 O.D.) and perhaps those on the Avon-Blythe watershed 

 and in the Warwickshire Coalfield and those capping isolated high hills 

 in the Avon vale, seem to belong to this early stage and to be the most 

 likely equivalents of the lower boulder clays of the Upper Avon valley 

 and of the Pennine drifts of the Trent, Soar, and Wreak valleys 



(Fig. 4, 5 and 7)- ^ . 



If we accept this view, it follows that the retreat of this First Welsh 



Glacier was connected with the ' first interglacial ' episode for which we 

 have discussed the evidence in the Upper Avon valley. In the Lower 

 Severn vale the Bushley Green Terrace, containing a temperate shell 

 fauna and lying at a considerably lower level than the Woolridge Terrace, 

 appears to belong to this time. The Bushley Green correlates with the 

 Avon No. 5 Terrace of Miss Tomlinson, but for the following reasons I 

 picture the latter as somewhat later in date though graded to about the 

 same level : the Bushley Green Terrace deposits seem to be overlaid 

 by eastern boulder clay, whereas Avon No. 5 near Evesham lies in a valley 

 cut through eastern drifts, and is also clearly newer than the Ridgeway 

 deposits in which there are eastern elements. I have already given 

 reasons (p. 81) for believing that the eastern drifts referred to were 

 laid down during a rather brief advance of the eastern ice to near Tewkes- 

 bury (Fig. 2), and that a more considerable halt was made near Stratford — ■ 

 as described by Miss Tomlinson. On this view the Bushley Green and 

 Avon No. 5 Terraces cover the * first interglacial ' episode and the oncoming 

 and maximum stage of the Great Eastern glacier in the Avon vale. 



What then of the rest of the region ? There are certain data and 

 several lines of reasoning which in my opinion justify us in postulating 

 the existence during the Great Eastern Glaciation of a Welsh ice sheet 

 reaching across the Stour and Salwarpe valleys, and covering the Black 

 Country, East Worcestershire and the Warwickshire Plateau (Fig. 5). 

 There is, however, no clear-cut evidence to prove whether it was the 

 shrunken First Welsh or, as I think more likely, a Second Welsh ice-sheet 

 which, as the first interglacial epoch passed away, grew and invaded the 

 northern part of the same region, incorporating to some extent in its 

 deposits the drifts of the earlier advance. 



I will refer very briefly to some of the reasons for my view. First, 

 in the region in question there are, as I have already mentioned, a certain 

 number (perhaps 40 or 50 are known) of small Irish Sea erratics, in the 

 form of Scotch and Lake District rocks, whereas none ^ are known in the 

 deposits already allocated to the First Welsh glaciation. Their distribu- 

 tion is shown on Fig. 4. 



Secondly, the deposits in some cases occupy valleys that seem to have 

 been excavated below the levels of the oldest drift-sheet. For example, 

 Miss Tomlinson has described evidence for what she refers to as a ' Welsh 

 re-advance,' which brought a north-western ice-sheet into the Blythe 

 valley after the deposition of the drifts of its southern watershed, and at 

 the time of the Stratford stage of the Great Eastern glacier. 



° The Packwood and Rowington granite boulders are on the extreme limit of 

 the Second Welsh Sheet as shown on Fig. 4. 



