September 15, 192 1] 



NATURE 



91 



centre of storm development then as now, but the 

 anticyclone over northern Europe prevented these 

 storms from taking- their present northern track 

 and forced them into the Mediterranean, where 

 they brought increased rainfall and a "pluvial 

 period." These meteorological conditions are 

 indicated in Fig. i. (The illustrations are repro- 

 duced by permission of the Council of the Royal 

 Meteorological Society.) By reference to the esti- 

 mates of Penck and Bruckner in the Alps and to 

 the " geochronological " work of Baron de Geer 

 in Sweden, this map is considered to represent 

 conditions prevailing until about 18,000 B.C. 



The presence of the ice-sheet is attributed to 

 elevation in Scandinavia (see Nature, vol. 102, 

 P- 335J- ^^ ith the subsidence of the land the ice 



Phas«. 

 Tbe Contineotal Phase 

 Ibe Maritime Phase 

 Toe La.er Korest Piiase 

 The Peat-bog hha^ 

 The Present Pnase 



Climaie. 

 CvDtinental 

 Warm and moi&t 

 Warm and dry 

 Cooler aiid moister 

 Becoming drier 



Dale. 

 6000-4000 B.C. 

 4000-3000 B.C. 

 3000-1^00 B.C. 

 1800 B.C-JOO A.I> 



500 A. D.- Present 



Fig. I.— Pressure and temperature distribution al the close of the last glaciaiion. 



receded, slowly at first, then more rapidly, but 

 about 8000 B.C. and again at 5000 B.C.. when ele- 

 vation temporarily closed the connection between 

 the Baltic and the Atlantic, there were halts or 

 slight readvances forming: the great Scanian and- 

 Ragunda moraines. At the same time the Alpine 

 glaciers, which throughout seem to run parallel 

 with the Scandinavian, formed the moraines of the 

 Gschnitz and Daun stadia. 



Until 6000 B.C. the ice-sheet was still large 

 enough to maintain a border of dry Arctic condi- 

 tions on its southern edge, but the mean annual 

 temperature of southern Sweden rose from 17° F. 

 to 35° F. .After 6000 b.c. the Ice age is regarded 

 as oyer, and the subsequent climatic history can 

 be divided into a series of " phases," as follows: 

 NO. 2707. VOL. I08I 



About 6000 B.C. elevation closed the outlet to 

 the Baltic for the second time, converting it into 

 the large freshwater Ancyhis lake. This shutting 

 out of the Atlantic accentuated continental condi- 

 tions in Scandinavia. The winter climate was 

 severe ; at first during the formation of the 

 Ragunda moraines the summers were not 

 esf)ecially warm, but later they became hot and 

 dusty. The rainfall was scanty, and the general 

 climate resembled that of South-east Europe. 

 Throughout this phase Scandinavia was occupied 

 by a rich forest flora, and. towards the close con- 

 ditions were very favourable to 

 tree-growth. The hazel extended 

 several degrees north of its pres- 

 ent position and to higher levels, 

 indicating a July temperature 

 about seven degrees higher than 

 the present. But the ivy and yew, 

 the limits of which depend on the 

 winter rather than on the summer 

 temperature, showed no such ex- 

 tension, indicating that the win- 

 ters remained severe. The absence 

 of storms off the north-west coast 

 of Norway is shown by the 

 forests, which at this period 

 covered all the outermost islands 

 as far as the Ingo Islands off 

 North Cape. These islands are 

 now barren, and their afforesta- 

 tion indicates a drier and less 

 stormy climate than the present, 

 with a decreased frequency of 

 winds from the sea. These con- 

 tinental conditions, however, did 

 not extend so far west as Ireland. 

 As the glacial anticyclone de- 

 creased in intensity, depressions, 

 from the Atlantic began to take a 

 more northerly course, but were 

 held up near the British Isles and 

 materially increased the rainfall 

 there, forming the first peat-bogs 

 of the western coasts. It seems 

 probable, however, that southern and eastern Engf- 

 land largely escaped this damp period, sharing in 

 the dry climate of the Continent. 



About 4000 B.C. submergence once more allowed 

 the Atlantic waters to flow into the Ancyhis lake 

 through a wide strait, much broader than the pre- 

 sent outlet, forming the Litorina sea. which was 

 appreciably larger than the present Baltic, and the 

 Continental Phase gave place to a Maritime Phase, 

 ver}' moist and equable. Depressions now passed 

 freely into the Baltic region, rainfall was heavv. 

 and peat-bogs began to form over extensive areas. 

 This favourable climate was best developed in the 

 Baltic countries where submergence was greatest, 

 but the whole of the North Atlantic and neighbour- 

 ing parts of the Arctic shared in it to some extent. 



