GEOLOGY. ' 565 



how they exist and wax or wane during the course of centuries is PHYSICAL 

 GEOGRAPHY, which we propose to consider. 



This tree of knowledge includes some very important branches, almost 

 parent stems. As a magnificent oak spreads forth its brawny arms, with 

 smaller branches and twigs, each of these great branches being as large as 

 an ordinary tree, so Physical Geography includes other arms such as 

 Geology, Meteorology, Botany, and Physiology even Astronomy in its 

 comprehensive embrace. We find it is a difficult task to separate these 

 kindred sciences from the great tree. We may have therefore to refer to 

 earth, air, and water, and their various forms in hills and mountains, wind, 

 vapour, rain, glaciers, and sea. We must learn how this earth has been 

 gradually cooled, and what the various stages of its growth have done. We 



Fig. 637. Disintegrated granite. 



must consider plant and animal life upon our planet, and how the atmosphere 

 affects them. All this is Physical Geography, and its satellite sciences of 

 Geology, Meterology, " Climatology," Botany, and Physiology. 



" Everything must have a beginning," and the earth must have had a 

 beginning, although the actual manner of the physical creation of the planet 

 is a disputed fact. We are not about to discuss the religious side of the 

 question, although we should undoubtedly find that Biblical and Geologic 

 teaching run side by side towards the same end, and the testimony of the 

 earth and sky bears witness to the Divine hand that created the universe, 

 which we can trace back to the dim and distant ages when " the earth was 

 without form and void, and darkness was upon the face of the deep." 



With this brief preface, let us consider some of these aspects, and pick 

 up interesting facts from the ground. 



GEOLOGY. 



In the chemical and mineral sections of this volume we have heard 

 something concerning the formation of the globe and its composition, its 

 clays, rocks, etc. With these internal arrangements Chemistry and Miner- 

 alogy have dealt. Geology tells us about the external surface of the earth, 

 its stones and rocks, and how they were formed, and generally something 

 about the conformation of the crust of the earth, and its history. 



