C— GEOLOGY 79 



tinuation of the great spreads of Rutland and Northamptonshire so clearly 

 delineated on Harmer's famous map of English Erratics. From the Soar 

 and Anker valleys there is an extension into the Trent valley which is 

 overlapped by the sphere of the Irish Sea glaciation. More evidence is 

 required here before a boundary can be drawn with certainty, but it seems 

 probable that the Eastern ice extended across Needwood Forest. South- 

 wards, the ' Main Eastern ' drifts (of Miss Tomlinson) near Stratford-on- 

 Avon appear also to belong to the Chalky Boulder Clay Series. The same 

 is true of the ' Moreton Drift ' of the same author, though this can only 

 be linked with those of Stratford by a series of hill-top occurrences in the 

 otherwise drift-free vale of Avon. 



In the last of our three drift-covered areas, the Midland Plateau, it is 

 not easy to generalise about the distribution, composition and origin of 

 the drifts. Often they consist of 10-20 feet of pebbly clay, sands and 

 coarse gravel, but there are several districts where far thicker deposits 

 occur. In such cases the drifts may be sometimes sand and gravel, as, for 

 example, at Moxley near Wednesbury, Bustleholm near West Bromwich, 

 Moseley, in the Cole valley, at Rowney Green near Alvechurch, near Barnt 

 Green, at Wildmoor east of Belbroughton, and near Kingswinford. At 

 Moxley and Kingswinford the sands lie in channels. At other places 

 boulder clays come in in force, as at the new Hospital Centre at Edgbaston, 

 where there are three boulder clays with intervening sands and bedded 

 silts ; California, where the general section is pebbly drift on thick ' india- 

 rubber clays ' (probably lake deposits) which in turn overlie coarse sands 

 and gravel and a lower stony boulder clay ; Lower Frankley where Cross- 

 key first proved high level (800 O.D.) glacial clay with Welsh erratics ; 

 and Blackwell where typical stony till is at least 25 feet thick. Except the 

 California ' indiarubber clay ' all these boulder clays appear to be true 

 ground-moraine. 



Farther south most of the Warwickshire Plateau has a covering of 

 clayey gravel, sand and sometimes coarse gravel. The high-level drifts 

 of the Ridgeway and of the hill-tops of Worcestershire are chiefly sands 

 and gravels, ' fringe ' deposits as Jerome Harrison termed them, implying 

 that they were mainly periglacial in origin. On the Ridgeway there are 

 also areas of clayey ground-moraine. 



The composition of the drifts varies somewhat, but they always include 

 a great deal of Bunter material, both pebbles from the Middle Bunter and 

 quartz grains from the sandstones. Next perhaps in number are erratics 

 from the coalfields and from the Wrekin area (see Fig. 3). North Welsh 

 rocks are often common, many coming from the Berwyns and the Den- 

 bighshire Silurian country. Large boulders of Arenig (and ? Aran) origin 

 are common in the district stretching from Walsall through Birmingham 

 and Harborne, and over the Lickeys and Frankley to Bromsgrove. North 

 Welsh material is therefore the most striking of the common far-travelled 

 erratics, and for this reason it is appropriate to term these deposits the 

 Welsh Drifts. To them, however, an Irish Sea Glacier contributed 

 Scottish and Lake District erratics on an exiguous scale. The map 



