Ixii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



water deposits, sufficiently indicate that they can have been wafted 

 for no great distance from the sites on which they grew. Thus the 

 Sequoia ( Wellingtonia) Langsdorffii was once the most abundant tree 

 in the north of Grreenland, and its remains are found as far south 

 as the Miocene beds of Switzerland and Italy ; and this example of 

 a genus to which belong the largest trees ia the world, and which 

 once existed abundantly throughout the high latitudes, but espe- 

 cially in Iceland, is very nearly akin to Sequoia sempervlrens, one of 

 the two species which alone survive and which are exclusively con- 

 fined to California. It is, perhaps, yet more surprising to hear of the 

 beeches, chestnuts, oaks, and even vines which, in those far distant 

 days, combined with a rich undergrowth of shrubs and elegant ferns to 

 form a picture conti-asting in the highest degree with the modern 

 condition of that same Greenland, covered by one colossal glacier. 



In the Miocene period, the northern limit of the limes, the Taxo- 

 dia, and the Platani was the 79th degree of latitude, whilst that of the 

 pines and poplars, if we may judge from what we now see, would 

 reach 15 degrees further north than the Platani, or absolutely to the 

 pole, or, at all events, the nearest land thereto. The great change of 

 climate is rendered sufficiently obvious by observing that the present 

 northern limit of trees is the isothermal line which gives a mean 

 temperature of 10° C. (or 50° P.) in July, and which nearly coin- 

 cides with the parallel of 67 degrees north latitude, never, therefore, 

 entering within the polar circle ; whilst in those days it even at- 

 tained the pole. 



Founding his opinion on the character of the flora. Prof. Heer 

 concludes that the mean temperature of the year, in the Miocene 

 epoch, was, in North Greenland, about lat. 79°, 5° C. (41° P.), whilst 

 at the same period that of Switzerland would have been 21° C. 

 (69°-8 F.), making a difference of 16° C. (28°-8 F.). At the present 

 day the difference between the mean annual temperature of Swit- 

 zerland (lat. 47°), reduced to the level of the sea, and that of Spitz- 

 bergen (lat. 78°) is 20°-6 C. (37°-08F.), whence it is evident that 

 at the Miocene period the general climate of northern Europe was 

 more equable than now, and that the mean temperature diminished 

 at a lower rate than the present between the temperate zone and the 

 pole, having then been at the rate of 0°'5 C. (0°-9 F.), and being now 

 0°-66C. (l°-2 F.) for each degree of latitude. 



In endeavouring to find an explanation for these facts now placed 

 so distinctly before us. Prof. Heer has examined a long series of the 

 hypotheses which have from time to time been advanced. He de- 

 clines to admit, for a moment, any supposition of the displacement 

 of the poles, and objects as well to the older views as to the recently 

 propounded theory of our secretary, Mr. J. Evans, which seeks to 

 show that modifications of portions of the earth's crust may be at- 

 tended by an actual movement of that rigid envelope over its in- 

 ternal nucleus. 



Far more important, in the opinion of the Swiss botanist, is the 

 speculation so admirably reasoned out by Sir Charles Lyell, on 

 the climatal changes which must be produced by a new distribution 



