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 Palæozoic times indicate such conditions 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 established, there will hardly be dispute as to the climate of the earlier periods. Plants of living species which require not only a mild temperature, 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.[1] All these require not merely a warmth but an evenness of temperature that in such high latitudes is extraordinary; extraordinary and incomprehensible, if then, as now, the solar heat was wholly shut out for more than four months. It will help to realize the difficulty 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 due 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 obliquity, 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[2] says that the thermometer at his winter quarters fell in March to—73.7°. For thirteen consecutive days it showed—59°; for over five days—66½°. 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-
