SCIENCE-GOSSIF. 



327 



Isle of Portland ; Chesilton ; Dawlish ; Hope's 

 Nose, Torquay ; many occurrences on south and 

 north coasts of Devon and Cornwall ; and Porlock 

 Bay, where are found remains of a submarine 

 forest. 



Prestwich was unable to support Godwin Austen's 

 theory, which was supported by Lyell, that the 

 large palaeozoic and crystalline boulders found in 

 the raised beaches and in the bed of the Channel 

 had travelled along an old coast-line extending 

 between Normandy and Sussex. At present the 

 tidal movements carry pebbly beach up channel 

 west to east ; but the presence of chalk flints in 

 the Devon raised beaches indicates that the move- 

 ment of materials was from east to west at the 

 time of their formation. The Ramsgate fishermen 

 are constantly meeting with obstacles to their 

 trawling in the shape of granite and serpentine 

 blocks that strew the bed of the ocean. Prestwich, 

 therefore, concluded that such foreign blocks were 

 brought through the open Straits of Dover in the 

 arms of floes and bergs by a current from the 

 North Sea. Such ice-floes especially became 

 stranded in the bay that stretched from the west 

 coast of Sussex across to Bembridge. Clement 

 Reid has pointed out how great was the deposition 

 of these foreign blocks in this particular area, the 

 Solent River then being perhaps in existence, but 

 the strait of Spithead not yet having been formed. 

 It seemed most probable that the foreign boulders 

 of the raised beaches were derived from the 

 " crystalline, metamorphic, and palaeozoic rocks 

 of Norway," or some of them possibly came from 

 Germany and the Ardennes. 



The raised beaches may be regarded with 

 tolerable certainty as contemporaneous with the 

 lowest of the river drifts of the Thames and Sorame 

 Valleys, also with the fauna of the cave epoch, 

 and these are but little removed in time from 

 recent alluvial beds. The rubble or head, which 

 contains mammoth remains, is therefore, accord- 

 ing to this chronology, more recent than the latest 

 valley drifts. 



Certain drifts in the London basin, which Mr. 

 Whitaker places under " Doubtful Deposits," have 

 *' the appearance of a 'local wash," and many of 

 these drifts Prestwich places with the '■ head," 

 so far as the cause of them is concerned. The 

 character of the head depends entirely upon the 

 character of the local strata, and the fragments of 

 the harder portions of which it is composed are 

 sharp and angular. It follows the slopes of the 

 hills, and as it recedes from its base becomes sub- 

 angular. As it ranges from the chalk hills the 

 chalky element gradually disappears. The mass 

 takes the colour and composition of a tertiary loam 

 or brick earth. The fact that it contains the 

 remains of land shells and land animals forms a 

 sure guide in tracing the same formation inland or 

 elsewhere. Murchison called it the angular flint 

 drift, and considered it to have been caused by 



great waves of translation resulting from the sudden 

 elevation and breaking up of the Wealden area by 

 earthquake action ; but geologists do not now ajDpeal 

 to catastrophic action as an explanation of the de- 

 nudation of the Weald. 



Lyell considered that the head as it appears at 

 Brighton " might have been heaped up above the 

 sea-level in the delta of a river draining a region 

 of white chalk," with perhaps a slow subsidence 

 during accumulation. He thought that the large 

 blocks and angular flints might have been trans- 

 ported by the aid of ice, the river and its tribu- 

 taries being occasionally frozen over. This seems 

 the most reasonable explanation of " head." 



Mr. Clement Reid calls in the aid of a frozen 

 climate in ordei: to explain the origin of the 

 numerous and now waterless chalk valleys. With 

 the ground frozen in a winter of Arctic severity to 

 a depth of several hundred feet, the otherwise 

 permeable chalk would be rendered impermeable 

 to the summer rains, and the surface waters then, 

 according to Reid, carried down the angular chalky 

 debris which went to form the local coombe rock 

 in the valleys and " head." 



Prestwich thought that after the formation of 

 the raised beaches the land was temporarily raised 

 100 to 120 feet, and the sand dunes, vvhich 

 occasionally occur between the raised beach and 

 the head, were formed. Then came a submergence 

 of about 1,000 feet. Much of the blown sand was 

 denuded away, but the submergence did not last 

 long enough for the establishment of a marine 

 fauna. On the final uprise of the land which 

 followed, the deposition of the rubble drift com- 

 menced, being caused by the displacement from a 

 state of rest of a great body of water. In order 

 that the resulting formation, the head, .should be 

 in any way different from other deposits, I under- 

 stand Prestwich to mean that the rise was sudden 

 and the resulting wave-action was of a cataclysmic 

 nature. This without ice would no doubt be 

 sufficient to transport the trail of debris over the 

 West Sussex plain, with but a slight fall in the 

 surface. 



Clement Reid has extended the application of 

 his theory of the formation of frozen-soil gravels 

 to the gravels of the Thames Valley. These 

 terrace gravels, which we are accustomed to 

 regard as marking successive stages in the excava- 

 tion of the Thames Valley by the river, may, he 

 thinks, have after all been laid down contempo- 

 raneously at all heights, the determination of the 

 relative ages of such gravels by reference to 

 heights above Ordnance data being of no value 

 whatever. He believes that there were two distinct 

 periods of Arctic cold, as evidenced in the south 

 and east of England, and these were divided by a 

 mild episode when the characteristic Pleistocene 

 mammalian and moUuscan fauna inhabited this 

 country. The second glaciatiou not reaching 

 south of the Wash, the rain in non-glaciated areas 



