ON THE ERKATIC BLOCKS OF ENGLAND, WALES, AND IRELAND. 225 



The second question is, Are there any Midland glacial beds referable 

 to the period of glacial subsidence ? Two series of deposits and of 

 erratics also have to be taken into account — those representing the period 

 of subsidence and those representing the period of re-elevation. During 

 the gradual subsidence of the ice-covered land, erratics would be floated 

 off as its various points became successively immersed, and deposits would 

 also be formed at the sea-bottom. These middle glacial clays, sands, and 

 gravels occur at various points. Fossils have been found near Welling- 

 ton, Shropshire, Astarte borealis being among them. In beds at Lilies- 

 hall, Salop (463 feet), three arctic species occur. The upper boulder 

 clay (worked for bricks through the district) contains erratics, which 

 appear cleai-ly to have fallen into it, and altogether differs from the lower 

 bed. It is a mass accumulated during subsidence. 



The third question is. What signs are there of ice action during the 

 re-elevation of the land ? During the process of re-elevation the marine 

 clays and sands would be washed and re-sorted by currents, and the sea 

 would be covered by icebergs floating away from our present mountains, 

 which would then be islands in a glacial sea. The Midlands now consti- 

 tute a table- land. This table-land would at this period be the shallow part 

 of the sea against which icebergs would be stranded. At Icknield Street, 

 Birmingham, the rock has been smashed and a large collection of Welsh 

 erratics flung against it. One of the most marked characteristics of this 

 period would be the distribution of fragments from the present highlands 

 of the Midlands. The present highlands of the Midlands would then be 

 low-lying islands, which would be covered with ice. By the breaking 

 away of the ice-foot around them blocks would be distributed over the 

 Bea-bottom in their immediate neighbourhoods. Rowley Hill blocks are 

 found eight or nine miles off. Boulders torn from Charnwood are abun- 

 dantly spread over many acres for many miles, and must have been carried 

 by local ice. Fragments from the Malvern Hills have been scattered 

 through the plains around. 



Erratics from the mountains of Wales, the Lakes, and Scotland also 

 must have been brought by the icebergs travelling from those centres 

 as the mountains became higher and higher. The work done during 

 re-elevation must be distinguished from that done during subsidence. 



The surface erratic blocks, so remarkably developed in the Midlands, 

 cannot be roughly explained away in connection with any one portion of 

 the epoch, and present complicated problems. Some erratics now upon 

 the surface may have been originally imbedded in clays and sands, which 

 have been washed away, and have really belonged to the ancient boulder 

 clay. Erratics were dropped by icebergs during the submergence of the 

 land when there was a succession of ever- varying island boundaries. 

 Erratics were also dropped during re-elevation when there was an ever- 

 increasing moui tainous area from which they could be derived. 



Facts have to be noted in connection with the following points : — 



(i.) The origin of the erratics. — Some were derived from a distance — 

 i.e., from W. Scotland, the Lakes, and Wales. Others were of local origin 

 and of local range, as from Charnwood, Rowley, and Malvern. Others 

 mark the pushing in of the debris derived from chalky boulder clay. 



(ii.) The heights of erratics above the sea. — Erratics are found in the 

 Midlands on heights extending from comparatively low levels to 900 feet. 

 They could not therefore have been deposited in their present positions 

 at one and the same time. They must indicate a succession of events. 

 1886. Q 



