286 DISCOURSE ON THE STUDY 



gularity, and so distributed over time as to produce 

 none of those interregnums of chaotic anarchy which 

 we are apt to think (perhaps erroneously) great dis- 

 figurements of an order so beautiful and harmonious 

 as that of nature. 



(321.) But to estimate justly the effects of 

 causes now in action in geology is no easy task. 

 There is no a priori or deductive process by which 

 we can estimate the amount of the annual erosion, 

 for instance, of a continent by the action of meteoric 

 agents, rain, wind, frost, &c., nor the quantity of 

 destruction produced on its coasts by the direct 

 violence of the sea, nor the quantity of lava thrown 

 up per annum by volcanoes over the whole surface 

 of the earth, nor any similar effect. And to con- 

 sult experience on all such points is a slow and 

 painful process if rightly gone into, and a very fal- 

 lible one if only partially executed. Much, then, 

 at present must be left to opinion, and to that sort 

 of clear-judging tact which sometimes anticipates 

 experience ; but this ought not to stand in the way 

 of our making every possible effort to obtain accu- 

 rate information on such points, by which alone 

 geology can be rendered, if not an experimental 

 science, at least a science of that kind of active 

 observation which forms the nearest approach to it, 

 where actual experiment is impossible. 



(322.) Let us take, for example, the question, 

 " What is the actual direction in which changes of 

 relative level are taking place between the existing 

 continents and seas?" If we consult partial ex- 

 perience, that is, all the information that we possess 

 respecting ancient sea-marks, soundings, &c., we 



