36 PRESIDENTIAL ADDRESS. — SECTION B. 



in South Africa. Though exceptions of this kind may be 

 attributed to the effect of geographical conditions in influenc- 

 ing the oceanic and air currents, the details are exceedingly 

 difficult to ascertain and support by evidence. 



The conclusion which may be drawn from this brief consi- 

 deration of the evidence from South African geology in the 

 three questions chosen is that though this part of the globe 

 has experienced great changes since the earliest known sedi- 

 ments were laid down, yet those changes have not been 

 uniform in direction. While the activity of any one agent of 

 chang-e, such as vulcanism, has been great at certain times and 

 dormant at others, it has possibly at no time surpassed the 

 degree it attains in some quarters of the globe to-day. 



The uniformitarian theory has been a very good servant to 

 geology in checking excesses, and the opposition to it has 

 probably in all cases risen from the arguments put forward by 

 astronomers and physicists, who, by starting from a state of 

 things observed in other parts of the universe or reached by 

 retracing the steps indicated by the present relation of earth, 

 moon and sun, have shown that there must have been a time 

 when circumstances on the earth's surface were very different 

 from what they are now. It is obvious that geology must 

 provide the criteria by which alone these theories can be 

 judged, so far as they concern the period represented by the 

 stratified rocks. This saving clause may perhaps suggest the 

 reason why there have been so many conflicting' conclusions; 

 the time since the earliest known stratified rocks were formed 

 may be so short compared with the age of the earth itself that 

 the consequences of the very different conditions indicated by 

 astronomers may have left no recognisable trace in those rocks. 



