WHAT IS KNOWN OF THE EARTH. 815 



well to remember that great though the changes in human affairs 

 have been since the most remote epochs of which there are records 

 in monument or history, nothing indicates that within this period 

 there has occurred any appreciable modification of the main out- 

 lines of land and sea, or of the conditions of climate, or of the 

 general characters of living creatures. The distance that sepa- 

 rates us from those days is as nothing when compared to the re- 

 moteness of past geological ages. No numerical estimate on which 

 reliance can be placed has yet been made of the duration even of 

 that portion of geological time which is nearest to us ; and we can 

 say no more than that the earth's past history, as recorded in 

 what we now find upon it, or as inferred from what we find, prob- 

 ably extends over hundreds of thousands or millions of years. It 

 is through the facts of geography, as now acquired and inter- 

 preted, that the geologist is supplied with the means of arriving 

 at the true signification of much that occurred in past time, the 

 traces of which survive in physical features or organic forms. 

 He finds that the most important agencies in determining and 

 modifying the present conditions of existence on the earth, whether 

 as affecting inorganic nature or organic beings, are closely con- 

 nected with the actual distribution of land and sea, and the 

 configuration of the surface ; and he learns that it is through 

 these agencies that he must seek to unravel the intricacies of 

 the past. 



The study of geology, in its turn, enables the geographer to 

 understand many things that would otherwise be unintelligible 

 to him. He thus learns how the boundaries of sea and land have 

 been determined ; where connections formerly existing have been 

 severed ; how islands have risen from the ocean and may be sink- 

 ing below it ; to what causes are due the rocky coasts and head- 

 lands, the indentations of the coasts, the formation of bays and 

 fiords ; at what time and by what means mountains have been 

 raised up, plains laid out, valleys excavated, and the courses of riv- 

 ers and positions of lakes fixed ; and he is taught the constituents 

 and qualities of the materials forming the surface of the earth, of 

 the soil upon it, and of the minerals beneath it. And as a better 

 insight is obtained into the natural relations of the mountains, 

 the plains, the valleys, rivers, lakes, and seas, the conviction arises 

 that the ever-diversified details of the face of the globe are in no 

 sense accidents or fortuitous results, little worthy, as such, of ad- 

 miration unless for their picturesque forms or wonderful propor- 

 tions ; but that they are the direct, orderly, and necessary out- 

 come of the action of forces simple in themselves, and operating 

 in accordance with well-known and invariable physical and me- 

 chanical laws. The perception of general characteristics of struct- 

 ure among the various features of the earth's surface that pass 



