150 MAN AND THE GLACIAL PERIOD. 



So soon as this ridge (less than 500 feet above the sea) is 

 crossed, we find the deposits laid down by the glacier 

 change their character, and sands and gravels attain a 

 great predominance.* Near Bridgenorth, and. at other 

 places, hills composed of such materials attain an altitude 

 of 200 feet. From Shrewsbury via Burton, and thence, 

 in a semicircular sweep, through Bridgenorth and Enville, 

 there is an immense concentration of boulders and peb- 

 bles, such as to justify the designation of a terminal mo- 

 raine. To the southward, down the valley of the Severn, 

 existing information points to the occurrence merely of 

 such scattered pebbles as might have been carried down 

 by floods. In the district lying outside this moraine there 

 is a most interesting series of glacial deposits and of bould- 

 ers of an entirely different character. (See map.) 



" From the neighbourhood of Lichfield, through some 

 of the suburbs of Birmingham, and over Frankley Hill and 

 the Lickey Hills to Bromsgrove, there is a great accumu- 

 lation of Welsh erratics, from the neighbourhood, prob- 

 ably, of Arenig Mawr. 



" The late Professor Carvill Lewis suggested that these 

 Arenig rocks might have been derived from some adjacent 

 outcrop of Palaeozoic rocks — a suggestion having its justi- 

 fication in the discoveries that had been made of Cum- 

 brian rocks in the Midlands. To test the matter, an ex- 

 cavation was made at a point selected on Frankley Hill, 

 and a genuine boulder-clay was found, containing erratics 

 of the same type as those found upon the surface. 



" The explanation has since been offered that this bould- 

 er-clay was a marine deposit laid down during a period 

 of submerge nee. f Apart from the difficulty that the 

 boulder-clay displays none of the ordinary characteristics 

 of a marine deposition, but possesses a structure, or rather 



* Mackintosh, Q. J. G. S. 



f Proceedings of the Birmingham Philosophical Society, vol. vi, 

 Part I, p. 181. 



