148 PROFESSOR JAMES GEIKIE ON THE 



These oscillations of the sea-level did not terminate with the emergence of the land 

 after the formation of the 50-feet beach. There is evidence to show that subsequent to 

 the retreat of the small local glaciers (4) and the emergence of the land, our shores 

 extended seawards beyond their present limits, but how far we cannot tell. With this 

 epoch of re-emergence the climate again became more genial, our forests once more 

 attaining a greater vertical and horizontal range. Submergence then followed (25 to 30 

 feet beach) accompanied by colder and more humid conditions, which, while unfavourable 

 to forest growth, tended greatly to increase the spread of peat-bogs. We have no evi- 

 dence, however, to show that small local glaciers again appeared. Finally the sea retired, 

 and the present conditions ensued. 



It will be seen that the submergence which preceded and probably accompanied the 

 advent of the lesser wrier de glace (2) was greater than that which heralded the appear- 

 ance of the local ice-sheets (3), as that in turn exceeded the depression that accompanied 

 the latest local glaciers (4). There would seem, therefore, to be some causal connection 

 between cold climatic conditions and submergence. This is shown by the fact that not 

 only did depression immediately precede and accompany the appearance of ice-sheets and 

 glaciers, but the degree of submergence bore a remarkable relation to the extent of 

 glaciation. Many speculations have been indulged in as to the cause of this curious 

 connection between glaciation and depression ; these, however, I will not consider here. 

 None of the explanations hitherto advanced is satisfactory, but the question is one well 

 deserving the attention of physicists, and its solution would be of great service to 

 geology. 



A still larger question which the history of these times suggests is the cause of 

 climatic oscillations. I have maintained that the well-known theory advanced by James 

 Croll is the only one that seems to throw any light upon the subject, and the observa- 

 tions which have been made since I discussed the question at length, some fifteen years 

 ago, have added strength to that conviction. As Sir Eobert Ball has remarked, the 

 astronomical theory is really much stronger than Croll made it out to be. In his 

 recently-published work, The Cause of an Ice Age, Sir Robert says that the theory is so 

 thoroughly well based that there is no longer any ground for doubting its truth. " We 

 have even shown," he continues, " that the astronomical conditions are so definite that 

 astronomers are entitled to direct that vigorous search be instituted on this globe to 

 discover the traces of those vast climatic changes through which astronomy declares that 

 our earth must have passed." In concluding this paper, therefore, I may shortly indicate 

 how far the geological evidence seems to answer the requirements of the theory. 



Following Croll, we find that the last period of great eccentricity of the earth's orbit 

 extended over 1 GO, 000 years — the eccentricity reaching its highest value in the earlier 

 stages of the cycle. It is obvious that during this long cycle the precession of the 

 equinox must have completed seven revolutions. We might therefore expect to meet 

 with geological evidence of recurrent cold or glacial and genial or interglacial epochs ; and 

 not only so, but the records ought to show that the earlier glacial epoch or epochs were 



