GEOGRAPHY AND EVOLUTION. 195 



it is to its application to geography that I wish to direct your at- 

 tention. 



I desire here to remark that, in wliat I am about to say, I altogether 

 leave on one side all questions relating to the origin of matter, and of 

 the so-called forces of Nature which give rise to the properties of mat- 

 ter. In the present state of knowledge such subjects are, I conceive, 

 beyond the legitimate field of physical science, which is limited to dis- 

 cussions directly arising on facts within the reach of observation, or 

 on reasonings based on such facts. It is a necessary condition of the 

 progress of knowledge that the line between what properly is or is 

 not within the reach of human intelligence is ill defined, and that 

 opinions will vary as to where it should be drawn : for it is the 

 avowed and successful aim of science to keep this line constantly 

 shifting by pushing it forward ; many of the efforts made to do this 

 are no doubt founded in error, but all are deserving of respect that 

 are undertaken honestly. 



The conception of evolution is essentially that of a passage to the 

 state of things which observation shows us to exist now, from some 

 preceding state of things. Applied to geography, that is to say to 

 the present condition of the earth as a whole, it leads up to the con- 

 clusion that the existing outlines of sea and land have been caused 

 by modifications of j^reexisting oceans and continents, brought about 

 by the operation of forces which are still in action, and which have 

 acted from the most remote past of which we can conceive ; tliat all 

 the successive forms of the surface the depressions occupied by the 

 waters, and the elevations constituting mountain-chains are due to 

 these same forces ; tliat these have been set up, first, by the secular 

 loss of heat which accompanied the original cooling of the globe; and 

 second, by the annual and daily gain or loss of heat received from the 

 sun acting on the matter of which the earth and its atmosphere are 

 composed ; that all variations of climate are dependent on differences 

 in the condition of the surface; that the distribution of life on the 

 earth, and the vast varieties of its forms, are consequences of contem- 

 poraneous or antecedent changes of the forms of the surface and cli- 

 mate ; and thus that our planet as we now find it is the result of 

 modifications gradually brought about in its successive stages, by the 

 necessary action of the matter out of Avhich it has been formed, under 

 the influence of the matter which is external to it. 



I shall state briefly the grounds on which these conclusions are 

 based. 



So far as concerns the inorganic fabric of the earth, that view of 

 its past history which is based on the principle of the persistence of 

 all the forces of Nature may be said to be now universally adopted. 

 This teaches that the almost infinite variety of natural phenomena 

 arises from new combinations of old forms of matter, under the action 

 of new combinations of old forms of force. Its recofrnition has, how- 



