NATURE 



[September i, tqio 



the present time. Again, the Boulder Clay of the eastern 

 counties is crowded, as we have described, with pebbles 

 ol chalk, which generally are not of local origin, but 

 iiave come from north of the Wash. Whether from the 

 bed of a river or from a sea-beach, they are certainly 

 ■water-worn. But if pre-Glacial, the supply would be 

 quickly exhausted, so that they would usually be con- 

 fined to the lower part of the clay. As it is, though 

 perhaps they run larger here, they abound throughout. 

 The so-called moraines near York (supposed to have been 

 left by a glacier retreating up that valej, those in the 

 neighbourhood of Flamborough Head and of Sheringham 

 (regarded as relics of the North Sea ice-sheet), do not, 

 in my opinion, show any important difference in outline 

 from ordinary hills of sands and gravels, and their 

 materials are wholly unlike those of any indubitable 

 moraines that I have either seen or studied in photographs. 

 It may be said that the British glaciers passed over very 

 different rocks from the Alpine ; but the Swiss molasse 

 ought to have supplied abundant sand, and the older 

 interglacial gravels quantities of pebbles ; yet the differ- 

 ences between the morainic materials on the flank of the 

 Jura or near the town of Geneva and those close to the 

 foot of the Alps are varietal rather than specific. 



Some authorities, however, attribute such magnitude to 

 the ice-sheets radiating from Scandinavia that they depict 

 them, at the time of maximum extension, as not only 

 traversing the North .Sea bed and trespassing upon the 

 coast of England, but also radiating southward to over- 

 whelm Denmark and Holland, to invade northern 

 Germany and Poland, to obliterate Hanover, Berlin, and 

 Warsaw, and to stop but little short of Dresden and 

 'Cracow, while burying Russia on the east to within no 

 great distance of the Volga and on the south to the 

 neighbourhood of Kief. Their presence, however, so far 

 as I can ascertain, is inferred from evidence ' very similar 

 to that which we have discussed in the British lowlands. 

 That Scandinavia was at one time almost wholly buried 

 beneath snow and ice is indubitable ; it is equally so 

 that at the outset the land stood above its present level, 

 and that during the later stages of the Glacial Epoch 

 parts, at any rate of southern Norwav, had sunk down 

 to a maximum depth of 800 feet. In Germany, however, 

 erratics are scattered over its plain and stranded on the 

 slopes of the Harz and Riesengebirge up to about 1400 

 feet above sea-level. The glacial drifts of the lowlands 

 sometimes contain dislodged masses of neighbouring rocks 

 like those at Cromer, and we read of other indications 

 of ice action. I must, however, observe that since the 

 glacial deposits of Moen, Warnemiinde, and Riigen often 

 present not only close resemblances to those of our eastern 

 counties, but also very similar difficulties, it is not per- 

 missible to quote the one in support of the other, seeing 

 that the origin of each is equally dubious. Given a 

 sufficient " head " of ice in northern regions, it might 

 be possible to transfer the remains of organisms from 

 the bed of the Irish Sea to Moel Tryfaen, Macclesfield, 

 and Gloppa ; but at the last-named, if not at the others, 

 we must assume the existence of steadily alternating 

 currents in the lakes in order to explain the correspond- 

 ing bedding of the deposit. This, however, is not the 

 only difficulty. The " Irish Sea glacier " is supposed to 

 have been composed of streams from Ireland, south-west 

 Scotland, and the Lake District, of which the second 

 furnished the dominant contingent, the first-named not 

 producing any direct effect on the western coast of Great 

 Britain, and the third being made to feel its inferiority 

 and "shouldered in upon the mainland." But even if 

 this ever happened, ought not the W'elsh ice to have joined 

 issue with the invaders a good many miles to the north 

 of its own coast ?° W'elsh boulders, at any rate, are 

 * A valuable summary of it is given in " The Great Ice Age," J. Geikie, 

 ch. xxix., XXX. (t8q4) 



~ From Moel Tryfaen to the ne.arest point of Scotland is well over a 

 hundred miles, .nnd it is a few less than this distance from Gloppa to the 

 Lake District. In order to allow the Irish Sea ice-sheet to reach the top of 

 Moel Tr^'faen the glacier productive power of Snowdonia has been minimised 

 (Wright, "Man and the Glacial Epoch," pp. 171. 172). But the difference 

 between that and the .\renifi region is not great enough to nu-ike the one 

 incompe'ent to protect its own borderland while the other could .send an ice- 

 sheet^ which cojdd almost cover the Clent Hills and reach the neighbourhood 

 of Birmingham. Anglesey also, if we suppose a slieht elevation and a 

 te-nperature of 2g° at the «ea-level. would become a centre of ice-distribution 

 and an advance guard to North Wales. 



NO. 2 13 1, VOL. 84] 



common near the summit of Moel Tryfaen, and 1 have 

 no hesitation in saying that the pebbles of riebeckite-rock, 

 far from rare in its drifts, come from Mynydd Mawr, 

 hardly half a league to the E.S.E., and not from Ailsa 

 Craig. ^ 



As such frequent appeal is made to the superior volume 

 of the ice-sheet which poured from the northern hills 

 over the bed of the Irish Sea, I will compare in more 

 detail t'ne ice-producing capacities of the several districts. 

 The present temperature of West-Central Scotland may 

 be taken as 47°, its surface as averaging about 2500 feet, 

 rising occasionally to nearly 4000 feet above sea-level. 

 In the western part of the Southern Uplands the tempera- 

 ture is a degree higher, and the average for altitude at 

 most not above 1500 feet. In the Lake District and the 

 Northern Pennines the temperature is increased by another 

 degree, and the heights are, for the one 1800 feet with 

 a maximum of 3162 feet, for the other 1200 feet and 

 2892 feet. In North Wales the temperature is 50°, the 

 average height perhaps 2000 feet, and the culminating 

 point 3571 feet. For the purpose of comparing the ice- 

 producing powers of these districts, we may bring them 

 to one temperature by adding 300 feet to the height for 

 each degree below that of the Welsh region. This would 

 raise the average elevation of Central and Southern Scot- 

 land to 3400 feet and 2100 feet respectively, for the Lake 

 District and Northern Pennines to 2100 feet and 1500 feet. 

 We may picture to ourselves what this would mean, if 

 the snow-line were at the sea-level in North Wales, by 

 imagining Sono feet added to its height and comparing 

 it with the Alps. North Wales would then resemble a 

 part of that chain which had an average height of about 

 10,000 feet above sea-level, and culminated in a peak of 

 11,571 feet; the Lake District would hardly differ from 

 it ; the Northern Pennines would be like a range of about 

 qooo feet, its highest peak being 11,192 feet. Southern 

 Scotland would be much the same in average height as 

 the first and second, and would rise, though rarely, to 

 above 11,000 feet; the average in Central Scotland would 

 be about 11,400 feet, and the maximum about 13,000 feet. 

 Thus North Wales, the Lake District, and the Southern 

 Uplands would differ little in ice-productive power, while 

 Central Scotland would distinctly exceed them, but not 

 more than the group around the Finsteraarhorn does that 

 giving birth to the Rhone glacier. In one respect, how- 

 ever, all these districts would differ from the Alps — that, 

 at 8000 feet, the surface, instead of being furrowed with 

 valleys, small and great, would be a gently shelving 

 plateau, which would favour the formation of piedmont 

 glaciers. Still, unless we assume the present distribution 

 of rainfall to be completely altered (for w^hich I do not 

 know any reason), the relative magnitudes of the ice 

 coming from these centres (whether separate glaciers or 

 confluent sheels) could differ but little. Scotch ice would 

 not appreciably " shoulder inland " that from the Lake 

 District, nor would the Welsh ice be imprisoned within 

 its own valleys. 



During the last few years, however, the lake-hypothesis 

 of Carvill Lewis has been revived under a rather different 

 form by some English advocates .of land-ice. For instance, 

 the former presence of ice-dammed lakes is supposed to 

 be indicated in the upper parts of the Cleveland Hills by 

 certain overflow channels. I may be allowed to observe 

 that, though this view is the outcome of much acute 

 observation and reasoning,- it is wholly dependent upon 

 the ice-barriers already mentioned, and that if they dis- 

 solve before the dry light of sceptical criticism, the lakes 

 will " leave not a rack behind." I must also confess 

 that, to my eyes, the so-called " overflow channels " inuch 

 more closely resemble the remnants of ancient valley- 

 systems, formed by only moderately rapid rivers, which 

 have been isolated by the trespass of younger and more 

 energetic streams, and they suggest that the main features 

 of this picturesque upland were developed before rather 

 than after the beginning of the Glacial Epoch. I think 

 that even " Lake Pickering," though it has become an 

 accepted fact with several geologists of high repute, can 

 be more simply explained as a two-branched " valley of 



1 The boulders of picrite near Forth NoHa, from I.lanerchymedd, though 

 they have travelled southward, have moved mucti to the west. 

 ■J P. F. Kendall, (Juart. Journ. Geol. Soc. Iviii. (1902), 471. 



