202 ON THE DISTRIBUTION OF PLANTS. | 
and on gneiss and granite. At the same period Prof. Ste renraras 
has shown the coast oak “(Quercus sessiliflora) was much more ¢ 
mon in Denmark than it is now. And, finally, the peat aie "of 
Norway and Boh — Loon omen: tell us that hazel and wild 
cherries (Prunus avium), w e both — of the rich 
Py <r of the sunny screes, 8 mes much more common than now. 
d their nuts and stones in the peat of the bare and treeless 
ptm coast regions as well as in the bogs of the monotonous pine 
woods of the _— country, in places far from those where hazel 
and = cherries now grow. From this we conclude that the flora 
of the sunny kr with all their bosiitatul shrubs and trees, lime, 
beam trees, maple, elm, hazel, ash, apple, roses, &c., an all the 
rare Sears plants which grow with them, is a remnant of 
bygone glory, from an age when Southern Norway was “much richer 
in a deciduous trees than it is to-day, and when the species 
growing with them were = more gies tiful. In this manner ve 
ate oclistae is strengthened by the “hell. banks, the clays, and t 
peat. The rere localities are asylums for a = 
the floras of bygone 
As to ree ee of dich changes in climate, plants alone give 
We must take into consideration the alternating 
prt of oak -bogs, and the different levels of river-terraces and old 
shore-lines, which s suppose to be due to the same periodical 
changes of: climate.* This is not the place in which to dwell more 
fully « upon the probable cause of these changes. We know that the 
procession of the equinoxes causes the length of winter and summer to 
change every 10,500 years. In 10,500 years winter i is longer than 
summer, in the next 10,500 summer is longer than winter, and so 
on. The difference between the two seasons may rise to more than 
thirty days, when the eccentricity of the earth’s orbit attains its 
ighest ue. And, moreover, we know, as shown by Prof. Mohn, 
that in the North Atlantic the average strength of ree ——e south- 
west winds is almost thrice as great in winter as in su Fi 
the researches of Zoppietz it Soe ae that ocean- conse are the 
effects of the ruling winds; the ength of the current depends on 
time. If in 0,500 years there are many thousand winter days 
so 
much more he sing wind, and consequently during such 
— the warm current which washes our shores an makes our 
ct 
* Cfr. A. Blytt, “On Variations of Climate in the course of time,” in 
don 
pee ‘ Nature,’ July 8 and 15, 5, 1886. ion 
