354 THE POPULAR SCIENCE MONTHLY. 



were not so sensitive to cold as are their closely allied successors. 

 There is some force in this, but we must not give it too much weight, 

 for all progress in knowledge of the world's history is based upon the 

 belief that, in general, corals in Palaeozoic times indicate such condi- 

 tions as exist where we now find corals ; saurians, where we now find 

 saurians ; tree-ferns where we now find tree-ferns ; and so of other 

 organisms. As soon as we leave this principle, we are at sea without 

 a compass, and almost without a star to guide us. There is direct 

 evidence of the warmth of climate in the Tertiary, and, if this be es- 

 tablished, there will hardly be dispute as to the climate of the earlier 

 periods. Plants of living species which require not only a mild tem- 

 perature, but one of great evenness, have been found in very high 

 latitudes. In Spitzbergen, latitude 78 56', there have been found the 

 remains of a Miocene flora remarkable for its variety and luxuriance. 

 One species, Libocedrus decurrens (Heer), now lives with the redwoods 

 of California ; another now occurs in the Andes of Chili ; while a 

 third, according to Dr. Gray, is the common Taxodium, or cypress of 

 the Southern States. In Greenland, latitude 70, were found magnolias 

 and zamias.* All these require not merely a warmth but an evenness 

 of temperature that in such high latitudes is extraordinary ; extraor- 

 dinary and incomprehensible, if then, as now, the solar heat was 

 wholly shut out for more than four months. It will help to realize 

 the difiiculty of a uniform climate in regions 75 to 85 from the 

 equator, if we consider what now would be the effect of a four months 

 night covering the torrid zone, and remember that the cold of arctic 

 countries is not dne to their position, but to the absence of the sun's 

 rays caused thereby. The accumulated heat of summer, great as it 

 is at the equator, would soon be radiated into space, and, when the sun 

 returned, not a living plant or animal would remain to greet it. 



The effect would be no less fatal if the long nights occurred in a 

 zone extending, say, 20 north or south of the Gulf States. Consider 

 the effect produced now by a slight lengthening of the night, and then 

 say how complete would be the destruction if the night's duration 

 was increased from a few hours to four months ! 



In geological times, if the axis of the earth had its present ob- 

 liquity, the midwinter nights in Spitzbergen, where the plants I have 

 mentioned were found, were four months long. The resulting changes 

 of temperature must have been very great. At the present time they 

 are enormous. Captain "Nares f says that the thermometer at his win- 

 ter quarters fell in March to 73*7. For thirteen consecutive days it 

 showed 59 ; for over five days 66|. The variation between that 

 and summer must be something enormous, for Mr. Meech has shown in 

 his paper on " Solar Heat," published in the " Smithsonian Contributions 

 to Knowledge," that the amount of heat from the sun received in high- 



* Dana, " Manual of Geology," revised edition, p. 526. 

 f Captain Xares's report in "Nature," vol. xv, p. 35. 



