PART III 



PHYSIOGRAPHICAL GEOLOGY 

 CHAPTER XVII 



LAND SCULPTURE 



Physiographical geology is the study of the topographical feat- 

 ures of the earth, and of the means by which, and the manner in 

 which, they have been produced. 



This subject is primarily a department of physical geography, 

 but is of value to the geologist for the light which it throws upon 

 the historical development of the land surfaces, and upon features 

 of the past which are not recorded in the processes of sedimenta- 

 tion. The geographer endeavours to explain the topographical 

 forms of the land, and, in order to do this, he must show how 

 those forms have originated. The geologist, on the other hand, 

 makes use of the topography to determine what changes have 

 passed over the land, and in what order those changes have 

 occurred. The old method of reading geological history con- 

 cerned itself merely with the sedimentary accumulations and 

 igneous intrusions. This method has the defect of leaving us with- 

 out information regarding the changes of land surfaces (except 

 where transgressions of the sea are recorded in unconformities) 

 and the details of mountain- making. The physiographical method 

 supplements this by adding, in part, the required information con- 

 cerning the land surfaces. Each method is improved and strength- 

 ened when we use both of them together, and when we are able 



300 



