8 INTRODUCTION. 



thus formed in earlier times may be observed in very many 

 places, if we know how to look for them. Thus geology, 

 perhaps more than any other science, cultivates the habit 

 of field-observation ; not, indeed, that minute observation 

 required by mineralogy or botany, but that wider observa- 

 tion which gives interest to mountain-travel or even to 

 rambles over the hills in our vicinity. It cultivates also, 

 in an eminent degree, the habit of tracing effects to their 

 causes for the question ever present to the geologist is, 

 " How came it so ? " 



Great Divisions of Geology. We have said that the 

 history of the earth is recorded in its structure, and that 

 structure is understood by study of causes or processes 

 now in operation. We have thus outlined the great di- 

 visions of geology, and the order in which they must be 

 studied. We must study, first of all, causes and processes 

 now in operation about us everywhere, producing struc- 

 ture. This is called dynamical geology. Next, we must 

 study the rocky structure of the earth to as great a depth 

 as we can, and apply the previously acquired principles in 

 its interpretation ; for this structure has been produced 

 by similar processes acting through all previous time. 

 This is called structural geology. Only after this shall 

 we be prepared to take up the history of the changes 

 through which the earth has passed ; for this history is 

 revealed in structure. This is called historical geology. 



