OF GEOLOGICAL DYNAMICS. 95 



if the actual retardation were not due to the tides 

 its amount would be ten instead of twenty-two, by 

 observation and dynamical theory of the moon's 

 motion. Two feet of ice per century, therefore, 

 melted from the supposed polar ice caps would be 

 required to account for it by the melting of ice, or 

 fifty feet in the twenty-five centuries during which 

 it has taken place. If, then, Professor Huxley can 

 show that it is probable that ice to any such 

 extent as that has melted from polar regions, 

 giving a gradual rise of the average level of the 

 sea to the extent of three feet, in the last twenty- 

 five centuries, he would establish the probability of 

 another solution than tidal retardation to the 

 astronomical question put before us by Adams. 

 But the very fact that dynamical theory of the 

 tides leads me to look for rather a greater than a 

 less amount of retardation than the twenty-two 

 seconds which we have estimated, makes it prob- 

 able that no such considerable rising of the sea 

 level, if any rising at all, will be found to have 

 taken place. On this question we may, however, 

 fairly look for some positive evidence from the 



