Studies for Students 



THE MAPPING OF THE CRYSTALLINE SCHISTS. 



PART I.— METHODS. 



Introduction. 



Conventional geological maps a mixture of fact and theory in unknown propor- 

 tions. 



Outcrop maps needed to display the fact. 

 Fact. — The Observations. 



Routine field observations. 



Important additional observations. 

 Theory. — The Drawing of Boundaries and Coloring of Map. 



The canons of geological mapping in crystalline areas. 



Canons of mapping modified by basal assumptions. 



INTRODUCTION. 



Conventional geological maps a mixture of fact and theory 

 in unknown proportions. — -For areas of the crystalline schists no 

 person save the maker or some one familiar with the area rep- 

 resented, can form any estimate of the value of a geological 

 map. In proportions dependent not alone upon the worker and 

 his conditions, but upon the area itself, theory has been com- 

 pounded with fact, until the map represents not what is, but 

 what the maker thinks after a study more or less extended. 

 Unfortunate also it is that the thoroughness and detail of the 

 study is not revealed. It is true that a geological map may be 

 so constructed as to disclose at once an impossible condition, or 

 one so contrary to common experience as to excite suspicion, so 

 that von Decken, the greatest of German map makers, once said 

 that there were really but two classes of geological maps — those 

 that may be right and those that cannot be right. But on the 

 other hand, a map may be prepared with but little examination 

 upon the ground, which is quite as plausible in aspect, or it may 

 be even more plausible, than one prepared by a conscientious and 



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