Reviews — Dr. James Geikie^ syGreat Ice Age, 33 



glaciation. The Upper or Hessle Boulder-clay indicates the re- 

 appearance of a great mer-de-glace in the North Sea; the erratics in 

 this clay are also evidently from British rocks, and they show that 

 the ice-sheet hugged the coast and was prevented from flowing right 

 out to sea by the presence of the Scandinavian ice. 



Passing now to North-west England, Dr. Geikie still firmly 

 maintains that the Boulder-clays of this district are the ground- 

 moraines of ice that overflowed from the basin of the Irish Sea, and 

 he now considers that the " Middle Sands," formerly thought to be 

 high-level " marine drifts," are simply morainic materials carried 

 upwards to their present position by an ice-sheet — a view suggested 

 many years since by Goodchild and Belt, and strongly advocated 

 by the late Professor Carvell Lewis and others. Under the same 

 category of gravelly moraines are also placed the shelly gravels 

 described by Mr Nicholson from near Oswestry at levels of 900 to 

 1160 feet above the sea. The sands and gravels which in the Mid- 

 lands are so prominently developed, are regarded as the work of 

 torrential waters during the melting of the ice-sheet. The evidence 

 of interglacial beds in the maritime areas appears to indicate a sub- 

 mergence after the melting of the mer-de-glace, but its extent is 

 quite uncertain — probably it did not go beyond 300 or 400 feet. 



In an interesting chapter on the Drift Deposits of Southern 

 England the author refers to the "rubble-drift" or "head," the 

 origin of which has lately been attributed by Professor Prestwich 

 to marine action, which swept the materials from higher to lower 

 levels, whilst the land was being raised by comparatively rapid 

 jerks from an imagined subsidence of 1000 feet under the sea. As 

 no trace of a marine origin is shown in these deposits, and there is 

 no direct evidence of the presence of the sea, this hypothesis is by 

 no means convincing. A more probable explanation is that the 

 angular drift of the " head " has reached its present position by the 

 action of frost and melting snows, and the gradual forward move- 

 ment of saturated, thawing subsoils. It is reasonable to suppose 

 that at the time when the country north of the Thames was entirely 

 covered by an ice-sheet, the climate of the Southern districts was 

 sufficiently severe to have frozen the surface soil to some depth, and 

 to have allowed the accumulation of snow, and perhaps of thin fields 

 of ice,_ and by the melting of these deposits in the summers whilst 

 the soil was frozen, the present dry valleys in the Chalk might have 

 been eroded and beds like those of the Coombe-rock formed, as 

 suggested by Mr. C. Reid. 



Want^ of space prevents us from commenting on the author's 

 description of the glacial phenomena of Northern and Middle 

 Europe, of the Alpine Lands, and other portions of the Continent; 

 but the summary of this portion of the subject lays open so clearly 

 the succession of events which the evidence is considered to have 

 established that we venture to give a condensed version of it. 



I. Pre-Glacial Times. In the older Pliocene the sea, which 

 then covered considerable portions of the east and south of England 

 and parts of Belgium, Holland, and France, was tenanted by a fauna 



DECADE IV. VOL. 11. — NO. I. 3 



