28o 



NATURE 



[September i, 1910 



the Red Chalk from either Hunstanton, Speetoii, or some 

 part of the Lhicolnshh-e wolds being found as far south 

 as the northern heights of London. Even the chalk and 

 tlint, the former of which, especially in the. Upper Boulder 

 Clay, commonly occurs in well-worn pebbles, are frequently 

 not' the local, but the northern varieties. And with these 

 are mingled specimens from yet more distant sources — 

 Cheviot "porphyrites, .South .Scotch basalts, even some of 

 the crystalline rocks of the Highlands. Whatever was the 

 transporting agent, its general direction was southerly, 

 with a slight deflection towards the east m the last-named 

 cases. 



But the path of these erratics has been crossed by two 

 streams, one coming from the west, the other from the 

 east. On the western side of the Pennine watershed the 

 Shap granite rises at Wasdale Crag to a height of about 

 itioo feet above sea-level. Boulders from it have descended 

 the Eden valley to beyond Penrith ; they have travelled in 

 the opposite direction almost to Lancaster,' and a large 

 number of them have actually made their way near the 

 line of the Lake District watershed, across the upper 

 vallev of the Eden, and over the high pass of Stainmoor 

 Forest,- whence they descended into Upper Teesdale. 

 Subsequently the stream seems to have bifurcated, one 

 part passing straight out to the present sea-bed, by way 

 of the lower course of the Tees, to be afterwards driven 

 back on to the Yorkshire coast. The other part crossed 

 the low watershed between the Tees and the Ouse, 

 descended the Vale of York, and spread widely over the 

 plain." Shap boulders by some means penetrated into the 

 valleys tributary to the Ouse on its west bank, and they 

 have been observed as far to the south-east as Royston, 

 near Barnsley. It is noteworthy that Lake District rocks 

 have been occasionally recorded from Airedale and even 

 the neighbourhood of Colne, though the granite from 

 Shap has not been found there. The other stream started 

 from Scandinavia. Erratics, some of which must have 

 come from the north-western side of the Christiania Fjord, 

 occur on or near the coast from Essex to Yorkshire, and 

 occasionally even as far north as Aberdeen, while they 

 have been traced from the East Anglian coast to near 

 Ware, Hitchin, and Bedford.'' It may be important to 

 notice that these Scandinavian erratics are often water- 

 worn, like those dispersed over Denmark and parts of 

 northern Germany. 



On the western side of England the course of erratics 

 is not less remarkable. Boulders from south-western 

 Scotland, especially from the Kirkcudbright district, both 

 water-worn and angular, are scattered over the lowlands 

 as far south as Wolverhampton, Bridgnorth, and Church 

 Stretton. They may be traced along the border of North 

 Wales, occurring, as has been said, though generally 

 small, up to about 1300 feet on Moel Tryfaen, iioo feet 

 at Gloppa, and more than that height on the hills east of 

 Macclesfield. Boulders from the Lake District are 

 scattered over much the same area and attain the same 

 elevation, but extend, as might be expected, rather farther 

 to the east in Lancashire. They also have been found on 

 the eastern side of the Pennine watershed, perhaps the 

 most remarkable instances being in the dales of the Derby- 

 shire Derwent and on the adjacent hills as much as 1400 

 feet above the sea-level. ° A third remarkable stream of 

 erratics from the neighbourhood of the .'\renig mountains 

 extends from near the estuary of the Dee right across the 

 paths of the two streams from the north, its eastern 

 border passing near Rugelcy, Birmingham, and Broms- 

 grove. They also range high, occurring almost goo feet 

 above sea-level on Romsley Hill, north of the Clents, and 

 being common at Gloppa. Boulders also from the basalt 

 mass of Rowley Regis have travelled in some cases between 

 four and five miles, and in directions ranging from rather 

 west of south to north-east ; and, though the mass hardly 

 rises above the 700-feet contour line, one lies with an 

 Arenig boulder on Romsley Hill. From Charnwood 



1 k pebble of it is said to have been identified at Moel Tryfaen. 



~ The lowest part of the gap is about 1400 feet. .'V little to the south is 

 ano'her gap about 200 feet lower, but none of the boulders seem to have 

 taken that route. 



'•' A Ijoulder was even found above Grosmont in'the Eske valley, 345 feet 

 above sea-level. 



4 R. H. Rastall and J. Romanes, Quart. Journ. Geol. Soc, I.\v. {1909), 

 p. 246. 



5 Communication from Dr. H. Arnold-Bemrose. 



NO. 2 13 1, VOL. 84] 



Forest, the crags of which range up to about 850 feet 

 above sea-level, . boulders have started which have been 

 traced over an area to the south and west to a distance 

 of more than twenty miles. 



Such, then, are the facts which call for an interpreta- 

 tion. , More than one has been proposed ; but it will be 

 well, before discussing them, to arrive at some idea of the 

 climate of these islands during the colder part of the 

 Glacial Epoch. Unless that were associated with very 

 great changes in the distribution of sea and land in 

 northern and north-western Europe, we may assume that 

 neither the relative position. of the isotherms nor the dis- 

 tribution of precipitation would be very materially altered. 

 A general fall of temperature in the northern hemisphere 

 might so weaken the warmer ocean current from the south- 

 west that our coasts might be approached by a cold one 

 from the opposite direction.' But though these changes 

 might diminish the difference between the temperatures 

 of London and Leipzig, they would not make the former 

 colder than the latter. At the present day the snow-line 

 in the .Alps on either side of the Upper Rhone \"alley is 

 not far from 8000 feet above sea-level, and this corre- 

 sponds with a temperature of about 30°. Glaciers, how- 

 ever, are not generally formed until about 1000 feet 

 higher, where the temperature is approximately 27°. 

 Penck and Bruckner place this line during the coldest 

 part of the Ice .'Vge at about 4000 feet." In that case the 

 temperature of the Swiss lowland would be some 15° 

 lower than now, or near the freezing point. ^ If this fall 

 were general, it would bring back the small glaciers on 

 the Gran Sasso d'ltalia and Monte Rotondo in Corsica; 

 perhaps also among the higher parts of the Vosges and 

 .Schwarzwald.' In our own country it would give a 

 temperature of about 35° at Carnarvon and 23° on the 

 top of .Snowdon. of 32° at Fort William and 17-5° on the 

 top of Ben Nevis. If, in addition to this, the land were 

 boo feet higher than now {as it probably was, at any 

 late in the beginning of the Glacial Epoch), there would 

 be a further drop of 2°, so that glaciers would form in 

 the corries of Snowdon, and the region round Ben Nevis 

 might resemble the Oetzthal -\lps at the present day. 

 This change of itself would be insufficient, and any larger 

 drop in the ocean-level would have to be continental in 

 its effects, since we cannot assume a local upheaval of 

 much more than the above amount without seriously 

 interfering with the river system of North Central Europe. 

 But these changes, especially the former, might indirectly 

 diminish the abnormal warmth of winter on our north- 

 western coasts.* It is difficult to estimate the effect of 

 this. If it did no more than place Carnarvon on the 

 isotherm of Berlin (now lower by 2°), that would hardly 

 bring a glacier from the Snowdonian region down to the 

 sea. At the present time London is about 18° warmc 

 than a place in the same latitude near the Labrado- 

 coast or the mouth of the .^niur River, but the removal 

 of that difference would involve greater changes in th? 

 distribution of sea and land than seems possible at an 

 epoch, comparatively speaking, so recent. I am doubtfu 

 whether we can attribute to changed currents a reduction 

 in British teinperatures of so much as ii°; but, if we 

 did, this would amount to 28° from all causes, and give 

 a temperature of 20° to 22° at sea-level in England during 

 the coldest part of the Glacial Epoch.' That is no« 



1 Facts relating to this subject will be found in " C limate and Time," by 

 J. Croll, ch. ii. and iii. (1875). Of course the air currents would also be 

 affected, and perhaps diminish precipitation as the latitude increased. 



2 I.oc. cit , p 586, ct sii/. They say the snow-line, which would mean that 

 the temperature was only laMower than now; but as possibly this line 

 might then more nearly correspond with that of glacier formation, I will 

 provisionally accept the higher figures, especially since Corsica, the Apen- 



5, and some other localities in Europe, seem to require a reduction of 



rathe 



!tha 



ild be -^z's" at Zurich, 3i"6°at Bern, 34'i° at Geneva, about 39'o'' 

 on the plain of Piedmont, and 36*0° at Lyons. 



4 See for particulars the author's " Ice Work" (International Scientific 

 Series), p. 237. 



5 For much valuable information on these questions see a paper on Clim- 

 ate of the Pleistocene Epoch (F. W. Harmer, Quart. Journ. Geol. Soc, Ivii. 

 1901, p. 405). 



<j The present temperature in Ireland over the zone (from S. of Belfast to 

 N. of Galway Bay) which is supposed to have formed the divide of the cen- 

 tral snowfield may be given as from 49° to 50% nearlv the same as at the sea- 

 level in Carnarvonshire. Thus, though the district is less mountainous than 

 Wales, it would not need a greater reduction, for the snowfall would probably 

 be rather larger. But this reduction could hardly be less than 20°, for the 

 glaciers would have to form nearly at the present sea-level. 



