244 Proceedings of the Royal Physical Society. 



currence of analogous changes is expected by them in time 



to come The greater warmth that seems to have 



prevailed in some former periods of the world's history is not 

 to be ascribed to a greater degree of heat in the globe itself, 

 but to a different distribution of land and water. If we were 

 to imagine all the land to be collected together in equatorial 

 latitudes, and a few promontories only to project beyond the 

 thirtieth parallel, would be undoubtedly to suppose an ex- 

 treme result of geological change. But a mere approxima- 

 tion to such a state of things would be sufficient to cause a 

 general elevation of temperature. If there were no arctic 

 lands to chill the temperature and freeze the sea ; if the ab- 

 sorption of the sun s rays was in no region impeded, even in 

 winter, by a covering of snow, the mean heat of the earth's 

 crust would augment, the water of lakes and rivers would 

 be warmer in winter, and never chilled in summer by melt- 

 ing snow. A remarkable uniformity of climate would pre- 

 vail amid the archipelagos of the temperate and polar 

 oceans, where the tepid waters of equatorial currents would 

 freely circulate. We might expect, in the summer of the 

 great year, plants allied to genera now called tropical. 

 Forms now confined to arctic and temperate regions would 

 almost disappear ; coral reefs would be prolonged again 

 beyond the arctic circles, and droves of turtle might begin 

 again to wander through regions now tenanted by the walrus 

 and seal." 



There are some parts of this hypothesis with which we 

 cannot concur. In the first place, we cannot suppose it 

 possible that the tepid waters of equatorial currents would 

 freely circulate, at a time when, according to Sir Charles' 

 theory, the torrid zone was almost entirely occupied by 

 land. The amount of water warmed by the sun, and flow- 

 ing to the higher latitudes, necessarily depends on the ex- 

 tent of watery surface that is exposed to the influence of the 

 solar beam. If the torrid zone were almost entirely covered 

 with land, as he supposes it to have been in the period of 

 the earth's highest temperature, there could not possibly 

 have been any of those equatorial currents of which he 

 speaks as warming the archipelagos of the northern ocean. 



