102 SECTIONAL ADDRESSES. 
were always balanced or distributed as they now are. There was in 
Lyell’s statements nothing to indicate that denudation or earth-movement 
might not have been more active at periods of the past, that organic change 
might not accelerate or slow down, that there might not be variations in the 
trends of continental or oceanic development resulting in climatal and 
other changes, or that the very sources and intensities of energy from out- 
side or inside the earth might not seriously vary. Only, warrant must be 
found for all such suppositions with regard to the earth of the past from 
fuller study of the earth of the present. And if we recognise the inner 
spirit which inspired the eloquent words of Lyell, when he had grasped 
that Darwin had supplied the one missing idea, we cannot fail to see that his 
Uniformitarianism included evolution as one of the ‘ existing causes’ to 
be taken into consideration. 
The physiology of the earth, however, is that of a very complex 
organism, and we are sure that we do not yet know all the forces internal 
and external acting upon it, still less their relative value and intensity, their 
distribution and variation in the past, or the precise records which each is 
capable of imprinting on the rocks of the earth-crust. But it is becoming 
clearer that there has been a periodicity in the stages of development of the 
earth-crust, and that on these great pulses of earth life there have been im- 
posed innumerable waves of smaller cycles ; and that, on account of their 
interference with, or reinforcement of, one another, the simpler type of 
cyclic repetition which might have been looked for in the history is masked 
and broken and diversified by actual happenings of an infinite variety. 
Van Hise more than once complained of the tendency of geologists to adhere 
to single explanations of events, and advocated the necessity of considering 
the co-operation of many causes ; and it may well be that in many out- 
standing problems, such as past glacial or tropical periods, coral reefs, 
stages of earth movement, progression and regression of the oceans, we may 
find the ultimate explanation in the interaction of a number of ‘ true causes.’ 
Evolution. 
During the long period of time comprised in the history from the Cam- 
brian Period onwards, the slow and persistent evolution of plant and 
animal life went forward and left ample record in the rocks. To warrant a 
belief in organic evolution, we are no longer solely dependent on reasoning 
founded on existing organisms or on the facts of their ontogeny and 
distribution. As M. Marcellin Boule says in his work on Fossil Man, 
“,... pour tout ce qui a trait 4 l’évolution des étres organisés en général, 
le dernier mot doit rester 4 la Paléontologie quand cette science est en 
mesure de parler clairement. Les plus fins travaux anatomiques, les 
comparaisons les plus approfondies, les raisonnements les plus ingénieux 
sur la morphologie des étres actuels ne sauraient avoir la valeur démon- 
strative des documents tirés de la roche ow ils sont enfouis et disposés 
dans leur ordre chronologique méme.’* Although we are only too pain- 
fully aware of the innumerable chances that conspire to prevent an animal 
or plant from securing immortality by preservation as a fossil, the finding 
of better-preserved material, the more skilful preparation of it for examina- 
tion, and the application to it of refined biological methods, such as 
careful dissection and the serial sections of Professor Sollas, are giving 
* Marcellin Boule, Les Hommes Fossiles, 1923, p. 453. 
