402 



NATURE 



[February 24, 1898 



developed. An arc with one electrode of aluminium and one of 

 carbon allows the current to pass with greater ease from 

 aluminium to carbon, which is just the reverse of what happens 

 in the cell. — Influence of magnetism on the strength of electric 

 vacuum discharges, by A. Faalzow and F. Neesen. The dis- 

 charge was produced by a constant high-potential battery. When 

 the lines of force acted across the path of the current, the latter 

 was always enfeebled, and sometimes broken. When they acted 

 along the path, the magnetic field acted like an increase of 

 pressure of the gas, delaying both the setting-in of the discharge 

 and its extinction in the course of exhaustion. — Relation between 

 the positive light and the dark kathode space, by E. Wiede- 

 mann. When a positive wire anode is brought into the dark 

 kathode space, the resistance of the intervening gas is not 

 lessened but increased. The positive light bends back until 

 it merges in the negative glow. The same thing happens when 

 the anode is surrounded by a narrow tube. In every case, 

 the discharge traverses the positive strata and the negative glow 

 in succession before it enters the dark space —Simple demon- 

 stration of the Zeemann effect, by W. Konig. An emission 

 flame which can be placed in a strong magnetic field is viewed 

 through an absorption flame and a dichroiscope or a doubly- 

 refracting prism, which gives two images of the emission flame 

 side by side. On making the field one of the images brightens 

 up, owing to the length of its light waves being changed, and 

 therefore no longer absorbed by the absorption flame. — Magnetic 

 and electric wind, by O. Lehmann. Describes some curious 

 cases of the modification of the path of an electric discharge by 

 a magnetic field. An arc between a ring of carbon and a con- 

 centric rod of carbon may be made to spin round rapidly, and a 

 comet-like appendage may be made to revolve round the kathode 

 in an " electric egg." 



MAN IN RELATION TO THE GLACIAL 

 PERIOD} 



A S there appears even now to be a doubt in the minds of 

 "**■ some as to whether man reached Britain before, during, 

 or after the time known to geologists as the " Glacial period," it 

 might be well on the present occasion to re-examine some of the 

 evidence which has been brought forward to prove the presence 

 of pre-Glacial man, especially from those areas in Britain 

 which are now admitted to contain Glacial deposits, oi to have 

 been overspread by ice and snow in the Glacial period. 



The most important evidence yet obtained, is that which has 

 been furnished by the ossiferous caverns in the glaciated areas ; 

 but the occurrence in the same areas of the remains of extinct 

 mammalia, which are now admitted to have been contemporary 

 with the Cave Man, buried under great thicknesses of Glacial 

 deposits, must also have an important bearing on the question. 



All the evidence tends to show that the so-called Tertiary 

 and Quaternary periods merged gradually into each other, and 

 were not separated by any great break in Britain. The higher 

 mountains, before the close of the Tertiary period, must have 

 been covered in part by ice and snow, and the so-called Glacial 

 period can only have a chronological importance as indicating 

 the increased intensity and climax of that cold condition 

 gradually ushered in at the earlier time. For the same reason 

 there is no marked and definite line separating the fauna of the 

 Pliocene from that of the Pleistocene, for we find remains of 

 the animals of the warmer period closely associated with those 

 of the colder in the same deposits and under conditions which 

 show clearly that they lived in those areas at the same time. 



North Wales and the North-west of England. 



It is generally admitted that during the latter part of the 

 Pliocene period the mountains of North Wales stood at a con- 

 siderably higher elevation than they do at present ; therefore it 

 is but natural to suppose that during that time the streams which 

 flowed from them gradually deepened, widened, and also possibly 

 carved out some of the pre-Glacial valleys. The Carboniferous 

 limestone along the flanks of the mountains, which had at an 

 earlier time been much broken and crushed by earth-movements, 

 now suff^ered from the additional effects of subaerial action, and 

 wide fissures and caverns were gradually formed in it. In time 



_ i " Evidences of the Antiquity of Man furnished by Ossiferous Caverns 

 In Glaci.ted Districts in Britain." Abstract of Presidential Addre^^s to the 

 Geological S iciety, delivered at the annual meeting, February i8, by Dr. 

 H. Hicks, F.R.S. 



some of these, as the streams found outlets at lower levels, would 

 be left comparatively dry, and would then be suitable for habi- 

 tation by man and beast. 



In nearly all those caverns where remains of the extinct 

 animals and the implements of contemporary man have been 

 found, there is some amount of sediment underlying the remains. 

 This must have been left there by the streams or floods which 

 also deposited the materal which filled up the narrow descending 

 fissures, thereby making a fairly level floor to the caverns before 

 occupation. This material in every case, unless where there is 

 evidence of its having been subsequently disturbed, consists 

 entirely of such local materials as would be brought down by 

 the streams from the immediately adjoining higher ground. 

 When the higher caverns were first occupied by hyaenas it is 

 probable that there was comparatively little ice or snow on the 

 mountains, and many of the animals which lived in the valleys 

 and on the plains extending from them were southern types. 

 Gradually, however, as the cold increased, northern forms 

 appeared on the scene, and a comtjiingling of the two groups 

 took place. 



The geographical features in the west and north-west in later 

 Pliocene times may be briefly summarised as presenting high 

 mountainous areas in Wales, Cumberland, the South of Scotland, 

 and in parts of Ireland bordering the Irish Sea and St, George's 

 Channel, with extensive plains traversed by great rivers in the 

 areas now submerged, between the west coast of England and 

 Wales, and Ireland. The conditions here were then in every 

 way suitable to form feeding-grounds for herds of the great 

 mammalia, and indeed such as could never have been repeated 

 afterwards in these areas either in late Glacial or in post-Glacial 

 times. 



Animals from the south-east could reach these north-western 

 plains across Cheshire and the lowlands in the centre of 

 England, and others from the south by the plains on the west 

 coast of Wales. In this way northern and southern animals 

 would in a sense freely commingle and be afterwards driven to 

 more southern areas together as the cold increased, and the con- 

 ditions became more and more unsuitable to them. At first, in 

 the mountains bordering these plains, when only their higher 

 parts were covered with ice and snow, glaciers would occur 

 only in the higher valleys ; but as the cold increased they would 

 become confluent with those from adjoining areas, and in time 

 reach the plains and there coalesce to form, perhaps, as has 

 been suggested, one vast sheet reaching across from England to 

 Ireland. Most of the animals, ere the last stage had been 

 reached, would, of course, have disappeared from those parts 

 towards more suitable southern areas. 



That the foregoing is, in brief, the history of the incoming of 

 the Glacial period in the north-west is evident from the deposits 

 which have been found in and about the caverns, and in sections 

 at various points on the hills, in the valleys, and around the 

 coast of North Wales. 



Wherever the earlier materials have been preserved, especially 

 at high levels, they are seen to consist entirely of local 

 materials, i.e. such as would be derived from the immediate 

 neighbourhood, or carried down by streams or ice from the 

 adjoining higher ground. 



Over this, and partly mixed up with it in the areas not reached 

 by the northern ice, there is an admixture of materials from 

 other Welsh districts and in the valleys opening out to the north, 

 and along the coast there is the further admixture of erratics from 

 northern areas. It is an interesting fact that the boundary-line 

 in the Vale of Clwyd reached by the northern erratics is very 

 little more inland than the area in which the caverns we have 

 explored occur. 



Of the history of the subsequent changes I need say but little ; 

 but it seems to me that there is fairly good evidence to show that 

 a considerable subsidence did take place towards the close of the 

 Glacial period, and that this was afterwards followed by a certain 

 amount of upheaval in the same areas. 



The presence of such thick deposits of drift, below the level of 

 the sea, at the entrance to the Vale of Clwyd, with bones of the 

 early Pleistocene mammalia at the very base, is a fairly sure test 

 of a stage of subsidence, and it is also difficult to account for the 

 finding of numerous foraminifera in clays at a height of about 200 

 feet above present sea-level around the coast unless alternating 

 movements of subsidence and upheaval took place. The marine 

 sand with broken shells at high levels, formerly looked upon as 

 sure evidence of subsidence to that depth must not be relied 

 upon too confidently, as in no case has it been clearly shown 



NO. 1478, VOL. 57] 



