42 DR. NILS EKHOLM ON THE METEOROLOGICAL [Feb. 1902, 
America, may have approximately coincided with the geographical 
equator. 
As to the influence of this state of weather on the climate of the 
great Asiatic continent, I do not venture to express an opinion, and 
must leave that point for future consideration. 
Finally, I may add the following brief remarks. 
Trees grow now farther north in Siberia than in Scandinavia, as 
the summer is warmer in the first-named region. As shown by 
Dr. Gunnar Andersson, no trees can grow if the mean temperature 
of July does not amount to at least 50° Fahr., but if this condition 
is realized, excessive severity of the winter does not prevent their 
growth. 
With regard to my paper on the variations of the climate of the 
geological and historical past and their causes,’ I tried to prove, in 
agreement with Prof. Sv. Arrhenius, that the principal cause of 
these variations is to be found in the variations in the quantity of 
carbon-dioxide present in the atmosphere. I remarked” also that 
the principal cause of the gradual rise of temperature about the 
end of the Great Ice-Age must be attributed to a slow increase of 
the quantity of carbonic acid in the air. But as the changes in 
the obliquity of the ecliptic also cause noticeable variations in the 
summer-temperature of every country north of 45° lat. N., those 
variations must be taken into account as well. Now, considering 
the geological fact that the Swedish palaobotanists have found after 
the end ot the Great Ice-Age only one marked period of a type of 
vegetation richer and more southerly than the present one, namely, 
that which occurred 9000 years ago, we must assume that 48,000 
years ago the ice that covered Sweden during the Great Ice-Age had 
not thawed away completely, or at least had so lately thawed that 
a richer flora had not had sufficient time to establish itself. Thus 
the end of the Great Ice-Age cannot have occurred 
more than about 50,000 years ago. It may possibly have 
occurred later, but it seems not improbable that the exceptionally 
intense insolation which, according to the formula of Stockwell, must 
have taken place during the summers of the northern countries 
from 50,000 to 46,000 years ago contributed materially to the 
melting away of the ice-cap. With regard to this conclusion of 
mine, Mr. Harmer remarks ?: . 
‘It seems to me improbable that the close of the Glacial Period took place at 
so remote a date.’ 
Thus he considers the 50,000 years as a maximum value, which 
is just what I said in the words printed above. On the other 
hand, nearly all those Swedish geologists and paleobotanists who 
have carefully studied the Quaternary Epoch in Sweden, believe 
that a date of 50,000 years ago is not too remote for the end of 
the Glacial Period in that country, and some of their evaluations, 
* Quart. Journ. Roy, Met. Soc. vol. xxvii (1901) p. 1. 
2 Op. cit. p. 45: 
3 Quart. Journ. Geol. Soc. vol. lvii (1901) p. 474, feats 
= 
