352 



SCIENCE 



[N. S. Vol. XXV. No. 635 



geysers, can not be questioned. Whatever 

 part chemical action, the friction or collisions 

 connected with faults, or that accompanying 

 flexures of strata may have in generating heat, 

 that heat-generation must have been much 

 more active in times of higher original tem- 

 peratures and active mountain-making. It 

 seems as though, despite all contrary sugges- 

 tions thus far made, a higher temperature at 

 the earth's surface than exists at present, 

 within the geological ages covered by the 

 warm-temperate flora and fauna found also in 

 the arctic regions, may fairly be presumed on 

 physico-geological grounds alone. This rea- 

 sonable assumption forms the basis of Man- 

 son's theory of the ice age. 



It can not be doubtful that during any 

 highly heated condition of the globe, of what- 

 ever origin, the bulk of the water now gathered 

 in seas, lakes and rivers existed in the form 

 of vapor, which as it ascended was condensed 

 into a mass of clouds forming a thick spher- 

 oidal envelope all around. On the outside, 

 upper surface of this cloud-sphere the sun ex- 

 erted substantially the same zonal effects as it 

 now does upon the earth's surface, modified 

 mainly by the uniformity of the physical 

 nature of the cloud-surface, as against the 

 alternation of sea and land as they now exist, 

 and which by their differences in the absorp- 

 tion and radiation of heat, in heat capacity, 

 and in topographic features, modify pro- 

 foundly the typical, regular zonal order of 

 climates. The tropical belt with its strong 

 ascending currents, low barometer, and high 

 temperatures; the two adjoining arid belts 

 with descending currents and high barometer, 

 and the temperate zones to poleward of the 

 same, with variable but generally low barom- 

 eter, would be defined on the cloud-spheroid 

 as they are now on the earth's surface, but 

 with greater regularity, though perhaps less 

 sharply. It is also clear that, though not 

 directly influencing the temperature of the 

 earth's surface, the solar radiation would 

 act powerfully as a conservator of earth-heat, 

 compensating to some extent the radiation 

 into space from the cloud-surface, of the heat 

 carried up by convection currents. 



The general disposition of the rain-belts 

 would also be substantially as it is now, but 

 the amounts of rainfall would, in so thick a 

 cloud-cover, undoubtedly be greater than at 

 present. The isothermal spheroids or shells 

 corresponding to our present temperatures 

 would at first be at heights more considerable 

 than at present; but as the heat carried up 

 from the earth's surface was more and more 

 lost by radiation into space from the exterior 

 cloud-surface, the isothermal shells would 

 gradually descend, and the temperature of the 

 falling rains would become lower, so as under 

 favorable conditions to fall as snow. It is 

 clear that snowfall might occur at any period 

 of the earth's evolution on high mountain 

 ranges or plateaus, and there the accumula- 

 tion of snow might at any period have formed 

 nevees and glaciers with their well-known 

 effects. The earlier glaciations observed, es- 

 pecially in the Permian, are, therefore, quite 

 compatible with Manson's theory. Elevation 

 as a cause of glaciation must, however, be ac- 

 companied by its necessary correlative factor, 

 an abundant rainfall; a point frequently left 

 out of consideration in this connection. Lab- 

 rador is a conspicuous example of non-glacia- 

 tion from low precipitation. 



Owing to the higher radiating power of the 

 earth-surface as compared with the ocean, as 

 well as to its much lower specific heat, the 

 earth must have cooled more rapidly than the 

 oceans by radiation alone. In addition to 

 this, the water flowing from it into the seas 

 would carry off a large amount of heat. Even 

 while the ocean still received heat from its 

 bed, the land areas would be a cooling agency 

 especially for the ocean depths, while the warm 

 oceanic surface waters would be supplying 

 abundant vapor for precipitation on the rela- 

 tively colder land areas. The latter would 

 finally fall to so low a temperature as to receive 

 their precipitation in the form of snow, thus 

 inaugurating the glacial period, during which 

 the isothermal shell of say the freezing-point 

 of water, and below, descended near to the 

 earth's surface. As the ocean gradually also 

 cooled and evaporation diminished, the pro- 

 tecting cloud-envelope became thinner, first in 

 the tropics and the flanking belts of lesser 



