40 THE POLAR GLACIERS. 



ceased to exist. Therefore, if the world had been subjected to 

 only the same solar heat in ancient as in recent periods, there 

 must have been repeated glacial epochs ; and we should find the 

 bowlder, and the unsorted drift, and the scratched and polished 

 rocks, all through the stone presentations. But very few, if any, 

 such evidences have been found. 



Again, for a warm and exuberant climate to extend into the 

 arctic zone, there was necessary one of those great summers of 

 considerable eccentricity, without the excessive drainage which 

 an unusually large accumulation of ice in the opposite hemisphere 

 would necessitate. Each summer cycle of coal forests, or of 

 reptile monsters, implies, not only a long visit and a high evap- 

 orating power of the sun, but also the addition to the opposite 

 polar regions, of a weight of ice only sufficient to draw the 

 waters from a small part of the low and flat lands of the warmer 

 hemisphere. We have seen that periods of warm, perhaps even of 

 tropical climates in polar latitudes, intervened between the great 

 winters of the last glacial epoch. But they have left scarcely a 

 trace in the strata. They were the nearest approach possible, 

 with the sun-power of recent times, to the conditions which of 

 old brought out such a profusion of animal and vegetable life. 

 But the only result in the later periods was, that the earth was 

 unbalanced ; all the waters were either turned into ice, or were 

 following after it toward one of the poles; one side of the 

 world was a frozen waste, while the other was a burning waste. 



I think we cannot avoid the conclusion that the sun shone 

 with a far intenser power on the Carboniferous swamps and the 

 Oolitic shoals than on the gravel-hills of the Drift; that the 

 oceans of early times were wider and warmer than now, and cir- 

 culated more freely between the tropics and the polar seas ; and 

 that the heated and moisture-laden atmosphere retained the heat 

 and equalized the temperature between the equator and the poles 

 far more than at present. 



With these conditions, that is, with a greater sun-power and a 

 considerable eccentricity of the earth's orbit, I can conceive of a 

 rational explanation, that which I have not yet seen in the books, 

 of the formation of the coal-layers, alternated as they always are 



