TRANSACTIONS OF SECTION C. 735 



appear allowable. lu each branch of science hypothesis forms the nucleus for the 

 aggregation of observation, and as long as facts are assimilated and co-ordinated 

 we ought to follow our theory.' Now, my point is that the uniformitarian 

 hypothesis, as applied to the rocks we can examine, has assimilated and co-ordinated 

 so many facts in the past, and is assimilating and co-ordinating so many new dis- 

 coveries, that we should continue to follow it, rather than plunge into the trackless 

 waste of cosmogonical speculation in pursuit of what may after all prove to be a 

 will-o'-the-wisp. 



As an additional illustration of the want of agreement amongst mathematical 

 physicists on questions relating to the earth, I maj^ refer to certain papers by 

 Mr. Chree.* This author maintains that the modern theory of elasticity points 

 to the conclusion that if a spherical globe, composed of a nearly incompressible 

 elastic solid of the size of the earth, were set rotating as the earth is rotating, it 

 would take the form which the earth actually possesses. How is the question of 

 the fixity of the earth's axis affected by Mr. Chree's researches, and by the recent 

 observations which prove a simultaneous change of latitude, in opposite directions, 

 in Europe and at Honolulu ? If geological facts point to a shifting of the position 

 of the axis, is there any dynamical reason why they should not receive due con- 

 sideration? Geologists want as much freedom as possible. We do not object to 

 any limitations which are necessary in the interest of science, and we cordially 

 welcome, and as a matter of fact are largely dependent upon, assistance from other 

 departments of knowledge ; but those who would help us should bear in mind that 

 the problems we have still to solve are extremely difficult and complex, so that if 

 certain avenues of thought are closed on insufficient grounds by arguments of the 

 validity of which we are unable to judge, but which we are naturally disposed to 

 take on trust, the difficulties of our task may be greatly augmented and the 

 progress of science seriously retarded. So far as I can judge, there is no a priori 

 reason why we should believe that any of the rocks we now see were formed 

 during the earlier stages of planetary evolution. We are free to examine them 

 in our own way, and to draw on the bank of time to any extent that may seem 

 necessary. 



For some years past the greater part of my time has been devoted to a study 

 of the composition and structure of rocks, and it has occurred to me that I 

 might, on the present occasion, give expression to my views on the question as 

 to whether the present position of petrographical science necessitates any important 

 modification in the theoretical views introduced by the uniformitarian geologist.?. 

 Must we supplement the ideas of Hutton and Lyell by any reference to primordial 

 conditions when we endeavour to realise the manner in which the rocks we cau 

 see and handle were produced ? The question I propose to consider is not whether 

 some of these rocks may have been formed under physical conditions dilTerent from 

 those which now exist — life is too short to make a discussion of geological possi- 

 bilities a profitable pursuit — but whether the present state of petrographical science 

 renders uniformitarianism untenable as a working hypothesis ; and, if so, to what 

 extent. There is nothing original in what I am about to lay before you. All 

 that I propose to do is to select from the numerous facts and more or less conflict- 

 ing views bearing on the question I have stated a few of those which appear to 

 me to be of considerable importance. 



The sedimentary rocks contain the history of life upon the earth, and on this 

 account, as well as on account of their extensive development at the surface, they 

 have necessarily received an amount of attention which is out of all proportion to 

 their importance as constituent portions of the planet. They are, after all, only 

 skin deep. If they were totally removed from our globe its importance as a mem- 

 ber of the solar system would not be appreciably diminished. The general laws 

 governing the formation and deposition of these sediments have been fairly well 



' C. Chree, ' On Some Applications of Physics and Mathematics to Geology,' 

 Phil. Mag., vol. sxxii. (1891), pp. 233, 342. 



