Date of the Glacial and the Upper Miocene Period. 385 



absence of fossil remains corresponding to the glacial condition 

 of things which we now know also did prevail at that epoch, 

 would very likely come to the conclusion that the former part 

 of the Postpliocene period was a warm period ; whereas we, at 

 the present day, looking at the matter from a different stand- 

 point, declare that part to be a glacial epoch. No doubt, if the 

 beds formed during the cold periods of the glacial epoch could be 

 distinguished from those formed during the warm periods, the 

 fossil remains of the one would indicate a cold condition of climate, 

 and that of the other a warm condition; but still, taking the entire 

 epoch as a whole, the percentage of fossil remains indicative of a 

 warm condition would probably so much exceed that indicative 

 of a cold condition, that we should come to the conclusion that 

 the character of the climate, as a whole, during the epoch in ques- 

 tion was warm and equable. 



As geologists we have, as a rule, no means of arriving at a 

 knowledge of the character of the climate of any given period 

 but through an examination of the sea-bottoms belonging to 

 that period; for these contain all the evidence upon the subject. 

 But unless we exercise caution, we shall be very apt, in judging 

 of the climate of such a period, to fall into the same error that 

 we have just now seen one would naturally fall into were he 

 called upon to determine the character of the climate during the 

 glacial epoch from the character of the organic remains which 

 lie buried in our adjoining seas. 



In conclusion, during the past three millions of years there were 

 three periods when the excentricity attained a high value. These 

 three periods are represented in Tables II., III., and IV. The 

 first began about 2,630,000 years ago, and terminated about 

 2,460,000 years ago. The second began about 980,000 years ago, 

 and terminated about 720,000 years ago. The third began about 

 240,000 years ago, and terminated about 80,000 years ago. 



The third period, for reasons which have now been considered 

 at some length, I believe to have been that of the Glacial Epoch ; 

 the second in all probability was that of the Upper-Miocene pe- 

 riod ; and the first might probably correspond to the glacial 

 epoch of the Middle-Eocene period. 



From the commencement of the glacial epoch, 240,000 years 

 ago, back to the close of the glacial epoch of the Upper-Miocene 

 period, represented in Table III., there is an interval of 480,000 

 years. Taking the ordinary rate of subaerial denudation, as in- 

 dicated by the rate at which rivers carry the soil off the land, 

 which we have already seen is not less than about one foot in 

 6000 years*, it follows that about 80 feet must have been removed 

 off the face of the country during that long interval. It is there- 



* Phil. Mag. for May 1868, p. 379. Trans, of Glasgow Geol. Soc. 

 vol. iii. part. 1. 



Phil. Mag. S. 4. Vol. 36. No. 244. Nov. 1868. 2 C 



