560 Sir S. H. Hotcorth — Geological Sistory of the Baltic. 



those lands was when the Baltic bridge was broken. There may 

 have been a partial extinction of forms due to various causes, but 

 the climate of the land was at least tolerant of all the various living 

 beings which now exist there and which must have reached there 

 overland. 



It is necessary to emphasize this because the position has been 

 somewhat sophisticated by the efforts of the Northern botanists to 

 press certain local conditions into a general law. That general law 

 seems to me inapplicable, at all events, to the period which has 

 elapsed since the Litorina stage of the Baltic history began. It has 

 been often affirmed, for instance, on the authority of Steenstrup, that 

 the bogs of Denmark afford a kind of thermometrical standard of 

 change of climate, marked by the succession of the forests embedded 

 in them. At the bottom of all are pine trunks. The pine has long 

 ceased to grow in Denmark, and is not known traditionally there. 

 Above the pines come oak-trees. The oak is also an infrequent tree 

 in Denmark. The present forests of the country are composed of 

 beeches, and it is argued that this is the general law of succession of 

 these trees, the fact being that when we go to Norway we find that 

 the oaks underlie the pines. Thus, as Professor James Geikie says, 

 "Mr. Blytt has recorded that in South -Western and Southern 

 Norway oaks and alders occur at the bottom of the bog, which is of 

 variable thickness and formed of aquatic and marsh-loving plants. 

 Above this under portion comes a second forest laj'er, composed 

 chiefly of pines, which are, in their turn, buried under a second bed 

 of sphagnum peat. Lindsberg and others tell us of exactly similar 

 phenomena in the peat bogs of Scania. There, as in Norway, the 

 bottom forest beds are formed of leafy trees, while the upper ones 

 are chiefly coniferous " (" Prehistoric Europe," pp. 528-9). Professor 

 Geikie has tried to get over this difficulty, but quite unavailingly 

 (id., pp. 5, 35, 36). The fact is the succession of these trees was long 

 ago shown to be, not a test of climate, but of another thing altogether. 

 When the forest fires take place in the barren lands of America or in 

 Siberia, it is found that a forest of leafy trees nearly always succeeds 

 one of coniferous trees, and vice versa, and the explanation is that each 

 class of tree more or less exhausts the special products of the soil 

 suited to it, and thus gives a chance to its rivals to supplant it. Again, 

 the forests of beech which now grow so largely in Scania and Denmark 

 do not grow over the remains of the buried pines and oaks ; these lie 

 in bogs whose surface sustains a growth of birches. The beech 

 does not like such soil as bog earth, the deep clay in which the oak 

 luxuriates or the sand wastes where the pine thrives, but loves 

 chalky and marly soils and gravels. 



I take it that the distribution of the trees in these areas was always 

 rather dependent on the constituents of its subsoil and on whether it 

 was for the time being drained or very wet than otherwise, and was 

 always dominated by local circumstances. Thus the beech, instead 

 of being quite a new-comer into the North, was there from early 

 times, but did not thrive on bogs or in land where clay soil abounds, 

 and therefore the remains of beech do not naturally occur in the 



