396 PAST succession: the ceneosere. 



Hartz (1910) has also discovered two definite glacial horizons in the island 

 of Jutland, with indisputable evidence of a well-marked glacial period, both in 

 regard to time and temperature: 



The plant remains found in certain layers have been transported from else- 

 where and in consequence give no information as to the climatic conditions at 

 the time of deposition. In the fluvio-glacial layers, plant remains are all 

 arranged according to weight and size of seeds. Among the flowering plants 

 were arctic and subarctic Betula nana, Salix herbacea, Dryas octopetala, etc., 

 and temperate species, lAmnanthemum, Brasenia, Potentilla anserina, Ajuga 

 reptans, and Ranunculus repens. The plants have been washed together from 

 different places and are probably of very different ages. 



Rutot (1910) has reached the following conclusions in regard to the variations 

 of the Quaternary climate in Belgium: 



At the termination of the great Hesbayan period, Belgium became dry. 

 At the end of the Mousterian, the dry winds from the east became established, 

 and the temperature gradually cooled, with the result that the forest withdrew 

 to the valleys and steppe developed on the plateaux. During the lower 

 Aurignacian the cold increased, corresponding to the maximum of the Wiirm 

 period. At this time the vegetation was that of tundra. Beginning with 

 the close of the lower Aurignacian, the climate grew warmer and the country 

 again became clothed with steppe, while forest developed in the valley. 

 These conditions were maintained during the middle and upper Aurignacian 

 and the Solutrean. During the transition from the lower to the middle Magda- 

 lenian a cold climate more intense than that of the lower Aurignacian inter- 

 vened, and the country again assumed the character of a pronounced tundra. 

 Towards the close of the Magdalenian the cold moderated somewhat, and 

 the climate became humid as a consequence of the opening of the channel and 

 the invasion of the North Sea. This brought about the reappearance of steppe, 

 after which the cUmate moderated still more and became temperate, ushering 

 in the Recent period with its development of moors. 



Sernander (1910) has concluded from the study of several moors in south 

 Holstein that the limiting horizon between the early and later Sphagnum peat, 

 as well as the peat-layers themselves, was formed in the sub-Atlantic period, 

 and that the forest-peat found beneath this is sub-boreal: 



The limiting horizon of Weber is, according to the author, only a local em- 

 phasis of Calluna heath in the continuous development which the Sphagnum 

 peat passed through from the beginning to the end of the sub-Atlantic period. 

 Sernander (1911) likewise finds in North European moors with complete late 

 Quaternary sequence, that there are two dry period horizons more or less 

 clearly indicated. The lower comprises the last part of the Ancylus period, 

 and is regarded by the author as boreal. The upper extends from the time 

 of the "Ganggraber" to the Bronze period, and is sub-boreal. The bulk of the 

 peat-moors of to-day was laid down in the Litorina period, while the formation 

 during the Ancylus period was much smaller. The author assigns the stump- 

 layers containing Fagus silvatica to the latter part of the sub-boreal period, 

 namely, to the Bronze Age. 



Schulz (1910) has summarized his conclusions in regard to the five glacial 

 periods of Europe. From the present distribution of the flora of Germany he 

 concludes that there have been eight different climatic periods, four cool and 

 four dry, which have followed each other alternately. The fifth glacial period 



