Page:The origin of continents and oceans - Wegener, tr. Skerl - 1924.djvu/117

Rh ages. Likewise corals are only found to-day in waters the temperature of which never falls below 20° C. Also no reptiles could have lived in past polar climates, since they produce no bodily heat, and likewise no earth-worms, since these cannot exist in frozen soil. But amphibia, and particularly fresh-water fishes, which utilize the warmth of the water, and mammals, which produce their own temperature, etc., could certainly do so. It is impossible to adduce here all the facts which can be employed to determine in what climate a given fossil fauna or flora lived. Of course, all these indications, if taken separately, are very uncertain, for both animals and plants yield examples of astonishing adaptation to a climate entirely foreign to the family concerned. But here, just as in the calculation of the path of a meteorite from a great number of inexact estimates, the individual data can be quite uncertain, often inverted, and, notwithstanding, give in their sum a very reliable result, when treated according to the law of the compensation of errors.

There still remain the inorganic evidences of climate, which have the advantage of not being able to adapt themselves. Boulder-clay, scratched detritus, and polished rock-surfaces, especially if they occur in a similar manner over great areas, denote the activity of land-ice, and therefore a polar climate. Coal, ancient peat-bogs, can form at the most different temperatures, but only if there is excess of rainfall compared with evaporation; conversely, salt deposits can only be formed in arid climates, that is, those with predominant evaporation. Thick unfossiliferous sandstones are to be considered as of desert formation, the red-coloured corresponding more to the hot deserts and the yellow-coloured rather to the more temperate ones (compare the red laterite of the tropics, the red earths