THE EARTH'S SHAPE 



many lakes at the present time. These three layers 

 oyster beds, peat, and marl would be like a family 

 pedigree showing the history of the place. The bottom 

 layer of white marl would show that there was once a 

 lake. The next layer of peat would show that by the 

 growth of marshy vegetation the lake became choked up 

 and was gradually changed into a swamp and then a 

 morass. The other layer of oyster shells would show that 

 the ground was afterwards submerged by the sea. The 

 present condition of the ground would show that the sea 

 at last retired, and the place passed into dry land as it is 

 to-day. 



By such a method of examination we may frame for 

 ourselves pictures of the earth's surface long before 

 history began, or before man roamed the earth. It is for 

 this reason that geology has been called the science that 

 investigates the history of the earth. The records in 

 which this history is chronicled are the soils and rocks 

 underneath our feet. It is the task of the geologist so to 

 arrange and interpret these records as to show through 

 what successive changes the globe has passed, and how 

 the dry land came to wear the aspect which it presents at 

 the present time. 



To do this efficiently the geologist has to learn many 

 things. He has to observe very closely the changes which 

 are going on about him on the world's surface. Only in 

 so far as he makes himself acquainted with these sudden 

 changes can he hope to follow intelligently and success- 

 fully the story of earlier phases in the earth's progress. 

 Nor is it sufficient to observe, however closely, inanimate 



37 



