2 EARTH FEATURES AND THEIR MEANING 



in common usage includes the plant as well as the animal world, 

 or what is sometimes called paleobotany. In order to fix the 

 order of events in geological history, these biological studies are 

 necessary, for the pages of the record have many of them been 

 misplaced as a result of the vicissitudes of earth history, and the 

 remains of life in the rock layers supply a pagination from which 

 it is possible to correctly rearrange the misplaced pages. As com- 

 piled into a consecutive history of the earth since life appeared 

 upon it, we have the division of historical geology; though this 

 differs but little from stratigraphical geology, the emphasis in the 

 case of the former being placed on the history itself and in the 

 latter upon the arrangement of events the pagination of the 

 record. 



So far as they are known to us, the materials of which the 

 earth is composed are minerals grouped into various characteristic 

 aggregates known as rocks. Here the science is founded upon 

 mineralogy as well as chemistry, and a study of the rock materials 

 of the earth is designated petrographical geology or petrography. 

 The various rocks which enter into the composition of the earth's 

 outer shell the only portion known to us from direct observa- 

 tion are built into it in an architecture which, when carefully 

 studied, discloses important events in the earth's history. The 

 division of the science which is concerned with earth architecture 

 is geotectonic or structural geology. 



The study of earth features and their significance. The 

 features upon the surface of the earth have all their deep sig- 

 nificance, and if properly understood, a flood of light is thrown, 

 not only upon present conditions, but upon many chapters of the 

 earth's earlier history. Here the relation of our study to topog- 

 raphy and geography is very close, so that the lines of separa- 

 tion are but ill defined. The terms " physiographical geology," 

 "physiography," and " geomorphology " are concerned with the 

 configuration of the earth's surface its physiognomy and with 

 the genesis of its individual surface features. It is this ge- 

 netical side of physiography which separates it from topography 

 and lends it an absorbing interest, though it causes it to largely 

 overlap the division of dynamical geology or the study of 

 geological processes. In fact, the difference between dynamical 

 geology and physiography is largely one of emphasis, the stress 



