VOL. XVIII. (2) GLACIAL BOULDERS, BOURNVILLE 169 



long anticlinal form— the so-caUed South Staffordshire anti- 

 chnal— the long and somewhat curved axis of which ranges 

 roughly from south to north for a distance of some thirty 

 miles from north-east of Redditch to east of Stafford. This 

 Midland antichnal presents in miniature almost all the mam 

 physiographic features of the classical anticlinal of the Weald, 

 its streams rising, even at the present day, not far from the 

 median axis, and flowing centrifugally across the more levelled 

 centre parts of the ancient dome, cutting in vaUeys some- 

 times gorge-hke through that broken ring of high ground, 

 which to-day represents the less denuded parts of the dome, 

 on their way to the surrounding plains, defined by the long 

 north and south synchnal forms, whose axes are paraUel to 

 that of the great dome. 



In the Birmingham country also, as in the Wealden region, 

 the highest points are now situated on the upland ring, and 

 look out in one direction over the central hoUows, and in the 

 opposite direction over the broad surrounding plains. 



This complicated structure had a most important bearing 

 upon the movement of the great Ice-Sheet, and the courses 

 of its lobe-like glaciers, both during the advance and retreat 

 of the Ice-Sheet. And not only so, but it in a sense controlled 

 the direction in which boulders could be transported during 

 thfe advance, and left behind in the retreat. And last, but 

 by no means least, these surface-irregularities determined the 

 places of the as yet undefined ice-dammed lakes, in front of 

 the ice sheet, until the last northern waters possibly over- 

 flowed through the lowest grooves in the main watershed, 

 namely the cols of Kingswood and Tettenhall. 



The erratics occurring in the Birmingham country (with 

 the doubtful exceptions of certain flints) have all been trans- 

 ported for long distances from the north or the north-west, and, 

 as a rule, the greater the distance from which they have been 

 brought, the greater is their rarity. 



There are granites from the South of Scotland, and from 

 Eskdale in the Lake District, granophyres from the Butter- 

 mere country ; andesites, felsites, rhyoUtes and ashes from 



