and in the central part to the thirty-seventh (confluence of the Mississippi and Ohio Rivers). In the most different parts of the world, too, we have found traces of a great ice age, as in the Caucasus, Asia Minor, Syria, the Himalayas, India, Thian Shan, Altai, Atlas, on Mount Kenia and Kilimandjaro (both very near to the equator), in South Africa, Australia, New Zealand, Kerguelen, Falkland Islands, Patagonia, and other parts of South America. The geologists in general are inclined to think that these glaciations were simultaneous on the whole Earth;[1] and this most natural view would probably have been generally accepted, if the theory of Croll, which demands a genial age on the Southern hemisphere at the same time as an ice age on the Northern, and vice versa, had not influenced opinion. By measurements of the displacement of the snow-line we arrive at the result—and this is very concordant for different places—that the temperature at that time must have been 4°–5° C. lower than at present. The last glaciation must have taken place in rather recent times, geologically speaking; so that the human race certainly had appeared at that period. Certain American geologists hold the opinion that since the close of the ice age only some 7000 to 10,000 years have elapsed, but this most probably is greatly underestimated.
One may now ask, How much must the carbonic acid vary, according to our figures, in order that the temperature should attain the same values as in the tertiary and ice ages, respectively? A simple calculation shows that the temperature in the arctic regions would rise about 8° to 9° C., if the carbonic acid increased to 2.5 or 3 times its present value. In order to get the temperature of the ice age between the fortieth and fiftieth parallels, the carbonic acid in the air should sink to 0.62–0.55 of its present value (lowering of temperature 4°–5° C.). The demands of the geologists, that at the genial epochs the climate should be more uniform than now, accords very well with our theory. The geographical annual and diurnal ranges of temperature would be partly smoothed away, if the quantity of carbonic acid was augmented. The reverse would be the case (at least to a latitude of fifty degrees from the equator), if the carbonic acid diminished in amount. But in both these cases, I incline to think that the secondary action due to the regress or the progress of the snow-covering would play the most important rôle. The theory
- ↑ Neumayr, Erdgeschichte, p. 648; Nathorst, l. c. p. 992.
