398 



NA TURE 



[August i6, 1906 



already been challenged by Prof. P. F. Kendall.' The 

 erratics are not seen to pass under the clays with southern 

 mollusca, as there is a gap of about half a mile between 

 the two deposits, so that the succession cannot be proved 

 by direct superposition. But Mr. Reid urges that " another 

 method is available : lo observe the occurrence of material 

 derived from the one stratum and redeposited in the other." 

 " No fragments of southern mollusca have yet been found 

 in the erratic gravel," but the clays with southern mollusca 

 often contained redeposited erratics. The gravel with 

 erratic blocks is, therefore, the older of the two." The 

 bed overlying the shelly deposit also contains erratics, and 

 these, too, Mr. Reid considers to be "redeposited"; but 

 it appears to me that the grounds for this inference are 

 insufficient. By (jodwin-.'\usten,^ who had previously de- 

 scribed the section, it was considered that the horizon of 

 the boulders was above the shell-bed ; and, since the shelly 

 deposit itself does not appear to exceed a few feet in 

 thickness, it is probable that heavy stones dropped on the 

 sea-floor by floating ice would embed themselves in the 

 shelly mud. 



Mr. Reid's suggestion that Ihe shell-bed may represent 

 a warm interglacial epoch newer than the glaciation in- 

 dicated by the Chalky boulder-clay, and therefore newer 

 than the so-called " middle glacial " of Northern England, 

 or than the Helvetian Kpoch of Prof. Geikie's scheme, 

 adds further confusion to the issue ; and the presence of 

 estuarine and freshwater deposits on the same coast, at 

 West Wittering and at Stone, in Hampshire, also regarded 

 as belonging to the same interglacial episode, raises 

 additional difficulties. 



Without entering at length into the matter, I can only 

 state that in my opinion, after full consideration of the 

 records, these South Coast sections do not afford definite 

 proof of a mild interglacial episode. 



Some Deposits above the Hoiilder-clays. — The frcshw^ater 

 deposits at Hoxne,' in Suffolk, and at Hitchin, in Hert- 

 fordshire,' classed bv -Mr. Reid as interglacial, belong to 

 a different category. They occur w-ithin the region of 

 actual glaciation, but in both cases it has been proved by 

 Mr. Reid that the beds overlie the Chalky boulder-day; 

 and there has bsen no subsequent glaciation of the district. 

 .At Hoxne, however, though not at Hitchin, the remains 

 of arctic plants are found in one part of the series, over- 

 lying deposits containing temperate plants. It is to be 

 noted, however, that several of the temperate plants occur 

 also in the arctic plant-bed, but are supposed to have been 

 derived from the older deposit. 



Under the usual classification of the field-geologist, the 

 whole series would be regarded as late-glacial or post- 

 glacial. At any rate, being above the Chalky boulder- 

 clay, they cannot belong to the supposed middle glacial, 

 or Helvetian Epoch ; and as the arctic plant-bed of Hoxne 

 is classed by Mr. Reid' as "Late Glacial," along with 

 other plant-beds with a similar flora which lie directly 

 upon the glacial drift in many parts of Britain, it is diffi- 

 cult to know where, in the English glacial sequence, we 

 are to place the supposed interglacial epoch represented by 

 the temperate plant-beds of Hoxne and Hitchin. 



From such deposits we regain at the most a mere frag- 

 ment of the whole flora of the time ; and I think there 

 is a danger that we lay too much weight upon accidental 

 instances of preservation. Is it not possible that the 

 northern flora lingered for some time in suitable places 

 alongside the re-advancing temperate plants? That some 

 minor oscillations of climate have occurred during post- 

 glacial times may be admitted ; but, so far as my experi- 

 ence has reached. I have not yet seen any evidence for a 

 general reversal of climatic conditions after the accumu- 

 lation of the Upper boulder-clay of eastern and western 

 England. 



I " The Cause of the Ice Age. ' Tratis. Leeds Geo/. Assoc, pt. viii. (1893), 

 p 64 



- Godwin-Au-sten, howevr. found southern shells in the Pholas-borings 

 which Mr. Rpid assigns to the supposed glacial deposit : ifi/ra cit. 



:< R. Godwin-Austen "On the Newer TertJarv Deposits of the Sussex 

 Coast." Quart. Jour,: C„-ot .^oc-. vol, xiii. (1857). pn. 40-72. 



■* " Report of Committee on Relation of Palseolithic Man to the Glacial 

 Period." Rtp. Br!t. .Assoc, for 1806, Dp. 400-415. 



5 '■ The Palaeolithic Deposits at Hitchin and their Relation to the Glacial 

 Enoch." Proc. Rov .Soc , vol. 1«1. (1807), pp. 40-ig. 



'' " Origin of the British Flora," supra cit., p. 53. 



NO. 1920, VOL. 74] 



ScoTL.iND. — The .Scottish evidence still remains to be 

 considered, and I must confess to a certain timidity in 

 venturing across the Border into this stronghold of the 

 " Interglacialismus," especially as my personal acquaint- 

 ance with the .Scottish drifts is slight. But, armed with 

 the experience gained south of the Border, 1 will attempt 

 the raid. 



On the eastern side of Scotland the drifts broadly 

 resemble those of the east of England ; while in western 

 Scotland they appear to be more nearly akin to those of 

 Wales and the west of Ireland ; with this difference, that 

 there is more plentiful evidence for local valley-glaciers 

 during the waning stages of the Glacial Period. 



The evidence for the Helvetian Epoch of deglaciation in 

 .Scotland is even more confused and indefinite than in 

 England. Some sporadic patches of peaty and silty 

 material associated with the boulder-clay are supposed to 

 represent a continuous land surface during an epoch when 

 previous ice-sheets had entirely melted away ; and similar 

 patches of marine origin are interpreted as the product of 

 a Helvetian submergence with which this interglacial 

 episode terminated. But the evidence is so widely scattered 

 and so diverse in character that it leaves us sceptical, in 

 spite of the admirable skill with which its arrangement 

 into the scheme is effected. 



The land deposits, almost without exception, were 

 observed in temporary exposures of small extent that are 

 not available for further study, and in several instances 

 doubt has arisen as to their exact relations with the 

 boulder-clay. The " elephant-bed " at Kilmaurs, .\yrshire. 

 appears generally to have underlain the boulder-clay, and 

 was originally supposed to be pre-glacial, though on other 

 evidence it is regarded as intercalated betw'een two bouldcr- 

 davs where both happen to be present.' The plant-bed 

 near .Airdrie, Lanarkshire, as we learn from the careful 

 description of the late James Bennie," occurred in wisps 

 in the boulder-day, and was evidently displaced ; and, 

 moreover, as in other of these Scottish plant-beds, the flora 

 is of arctic character. There are, in fact, according to 

 Mr. C. Reid, only three localities at present known in 

 Scotland where plants indicative of a temperate climate 

 have been discovered in beds supposed to be intercalated 

 with boulder-clay, viz., Cowden Glen (Renfrew), Redhall, 

 and Hailes (both near Edinburgh), and in each case Mr. 

 Reid has found such anomalous results in his critical 

 examination of the plant remains said to have been obtained 

 from the deposits that, in spite of his usual willingness to 

 adopt the Interglacial hypothesis, he has been led to doubt 

 the evidence for their " interglacial " position.' Prof. J. 

 Geikie. it is true, has challenged Mr. Reid's results ; * and 

 as it is staled that the Cowden Glen section has been 

 obliterated for many vears, the Hailes interglacial deposit 

 long since reinoved. and the Redhall quarrv now obscure, 

 there seems no likelihood of further evidence on either 

 side ; which is the more to be regretted in view of the 

 curious circumstance, already commented on, that not a 

 single interglacial peat-bed has ever been detected in all. 

 the length of our unrivalled coast sections. As the matter 

 stands, we are, I think, justified in regarding these Scottish 

 land deposits as an insecure foundation for the wide- 

 reaching conclusions which have been drawn from them. 



The hypothetical Helvetian submergence of Scotland 

 rests on similar evidence to that which has been already 

 discussed in the case of the English and Irish drifts. Its 

 limits arc not marked by any shore-line, and, indeed, are 

 acknowledged to be uncertain by Prof. Geikie himself. 

 Some patches of marine sediments, containing a molluscan 

 fauna that is generally distinctly boreal, have been found, 

 sometimes beneath, sometimes above, and sometimes inter- 

 calated with the boulder-clay ; but it is especially note- 

 worthy that these patches all occur along the outer inargin 

 of the country, contiguous to the sea-basins, and that n 

 belt of shelly boulder-clay, denoting the dispersal of pre- 



1 "Great Ice Affe,"' 3rd ed . op. 133=5. 



2 "On the Occurrence of Peat with Arctic Plants in Boulder Clay at 

 Faskine. near Airdrie." Trans. Geol. Soc., Glttsgoiv, vol. x. (1894), 

 pp 148-152. 



^"On Scottish Interglacial Deposits.' Geol. Mag., dec. iv., vol. 11. 

 1895). pp. 1-3- 



-• "Scottish Interglacial Beds" ^letter). GeoL Mn^., dec. iv., vol.11. 

 (1S05), pp. 2S3-4. 



