“Corresponding regions in South America are in parts characterized by an even higher humidity. In Iquitos by the Amazon River, it reaches not less than 83 per cent. of saturation. The annual change of temperature is only about 5° C. (9° F.); in Para (1.08° south latitude on the coast) it shrinks to 1° or 1.5° C. (1.8° to 2.7° F.). In the course of twenty-four hours the variation is considerably larger. The sky is remarkably clear between showers during the rainy season. In the interior of Guiana, the rains continue from the end of April well into July or even into August. Abundant dew is common during the rainless part of the year, thus maintaining the humidity. Sun and Moon are rarely visible, and gigantic lightning storms announce the arrival of the rainy period.”
Similar conditions apparently prevailed during the carboniferous period, which was characterized by a luxuriant vegetation. The mighty tree-trunks of that time fell into the water-covered marshes out of which they had grown and their decay was thereby prevented. Instead they turned into coal like the peat in the mosses of today. This was for some time thought to indicate that the temperature was not particularly high--Frech estimated about 12° C. (53.6° F.) (1910). But since the discovery and subsequent description by Keilhack (1914) of peat-beds on Ceylon, where the average yearly temperature is 26° C. (78.8° F.), a return is to be expected to the older conception, which held that the vegetation during the carboniferous period is evidence of a very warm climate. Judging by the appearance of fossil plants, the temperature should have been nearly the same all over the globe. Carthaus remarks that the air was stirred by only feeble winds because the trees of that age with their great dimensions but frail root-systems could not have withstood a fresh breeze. The sky was hidden behind a continuous thick cover of clouds which only let a faint light sift through to the ground. The motionless air was almost saturated with moisture. The luxuriance of the vegetation, transcending anything existing today, indicates a favourable high percentage of carbonic acid in the air. This combined with the humidity and the dense clouds caused the heat radiation from the Sun to be almost entirely absorbed by the upper strata of the atmosphere in which thereby a strong circulation was maintained. As a result, the heat was nearly equalized between the poles and the equator and under the cloud cover an almost constant temperature reigned day and night, summer and winter. The damp air stood wellnigh still and was filled with dense fog at the smallest changes in temperature. Lack of light prevented the development of flowers, and the thriving plants belonged mainly to the ferns and to the horsetails. Pine and fir trees were yet comparatively few. The conditions in the swampy regions where plant life flourished were nearly identical with those in a hothouse if we were to draw a dense veil in front of the windows in walls and ceiling so that a continuous twilight would prevail.