98 Prof. Hughes, Criticism of the Geological [Oct. 30, 



The Master of Downing College, V.P., in the Chair. 



The following Communication was made to the Society : — 



Criticison of the Geological evidence for the Recurrence of Ice 

 Ages. By the President (Professor Hughes). 



Part I. Condition of the surface of the Boulders 

 AND OF the Solid Rock. 



i. Introduction. 



To many of us the most interesting matter which has recently 

 been brought before this Society was the discussion of the cause 

 of the Glacial Epoch. But those who have been watching the 

 development of theory and the controversies which have arisen 

 out of the consideration of the question must feel that although it 

 is too large a subject to be treated as a whole at any one meeting 

 yet the several points in the long chain of evidence are of such a 

 nature as to lend themselves readily to separate discussion, and 

 that no view, founded upon such circumstantial evidence as that 

 on which every glacial theory depends, should be accepted until a 

 searching enquiry has been made into the value of the evidence for 

 each of the facts upon which it is based. 



I would state at the outset that I do not wish to divide the 

 advocates of the Geographical explanation and the supporters of 

 the Astronomical theory by a hard and fast line. I will acknowledge 

 that most of those who look upon astronomical combinations as the 

 principal cause allow that the distribution and height of the land 

 must have great influence though they may be pre23ared to admit 

 the possibility of freezing over the sea and then heaping snow on 

 until the accumulation of ice displaces all the water. 



On the other hand, among those who regard geographical con- 

 ditions as having had most to do with the determination of the 

 time and place of greatest glaciation, there are few who would 

 deny that climatal conditions must be affected by astronomical 

 changes, though they may regard these more or less in the same 

 light as they do lunisolar influences in volcanic eruptions. 



Whether we adopt the one view or the other, it is obvious that 

 the recurrence of glaciation may be regarded as probable. It has 

 however been maintained by some advocates of the astronomical 

 theory that, although the results were due to secularly recurring 

 combinations, it was only during the latest periods that the 

 requisite conditions prevailed to produce the full effect in 

 glaciation. 



The great difference between the two cases is this. On the 

 astronomical hypothesis the effect should be produced at intervals 



