4 EARTH FEATURES AND THEIR MEANING 



nomic geology " and " mining geology " have either a pedagogical 

 or a commercial significance, and so would hardly fit into the 

 system which we have outlined. 



-Geological processes not universal. It is inevitable that the 

 geology of regions which are easily accessible for study should 

 have absorbed the larger measure of attention; but it should not 

 be forgotten that geology is concerned with the history of the 

 entire world, and that perspective will be lost and erroneous 

 conclusions drawn if local conditions are kept too often before 

 the eyes. To illustrate by a single instance, the best studied 

 regions of the globe are those in which fairly abundant precipita- 

 tion in the form of rain has fitted the land for easy conditions of 

 life, and has thus permitted the development of a high civilization. 

 In degree, and to some extent also in kind, geologic processes 

 are markedly different within those widely extended regions which, 

 because either arid or cold, have been but ill fitted for human 

 habitation. Yet in the historical development of the earth, those 

 geologic processes which obtain in desert or polar regions are none 

 the less important because less often and less carefully observed. 



Change, and not stability, the order of nature. Man is ever 

 prone to emphasize the importance of apparent facts to the dis- 

 advantage of those less clearly revealed though equally potent. 

 The ancient notion of the terra firma, the safe and solid ground, 

 arose because of its contrast with the far more mobile bodies of 

 water ; but this illusion is quickly dispelled with the sudden quak- 

 ing of the ground. Experience has clearly shown that, both upon 

 and beneath the earth's surface, chemical and physical changes 

 are going on, subject to but little interruption. " The hills rock- 

 ribbed and ancient as the sun" is a poetical metaphor; for the 

 Himalayas, the loftiest mountains upon the globe, were, to speak 

 in geological terms, raised from the sea but yesterday. Even 

 to-day they are pushing up their heads, only to be relentlessly 

 planed down through the action of the atmosphere, of ice, and of 

 running water. Even more than has generally been supposed, the 

 earth suffers change. Often within the space of a few seconds, 

 to the accompaniment of a heavy earthquake, many square miles 

 of territory are bodily uplifted, while neighboring areas may be 

 relatively depressed. Thus change, and not stability, is the order 

 of nature. 



