994 Subsurface Geologic Methods 



d. Quantitative geologic values are represented as accurately as they 

 are determined in the field. 



e. It is possible to show gradational trends as well as abrupt changes; 

 where obscure and uncertain field relationships exist, the represen- 

 tation must be equally obscure and uncertain. 



f. Subtle values are magnified so that they are readily apparent on the 

 maps. 



g. Qualitative and quantitative values represented colorimetrically or 

 graphically are cumulative in terms of compositional trends, pro- 

 cess, time, and criteria of ore localization. Thus, all hydrothermal 

 effects are represented by similar colors so that highly hydrotherm- 

 alized areas are readily apparent and the total hydrothermal effect 

 is readily evaluated. 



h. An office-map system is such that economic or assay metallization 

 representation is quantitative, qualitative, graphic, cumulative. 

 Metallization may be readily integrated with the geologic repre- 

 sentation. 



5. All field-subsurface and office representation is accomplished on a basis 

 of factual data. McKinstry^ defines a map as 



a record of geological facts in their correct space relations— facts, be it 

 noted, not theories. There must always be sharp distinction between observa- 

 tion and inference. You can see a contact where it is exposed but you cannot 

 see it under covered ground. . . . This failure to distinguish between fact and 

 inference is a criticism tliat can justly be leveled at some of the otherwise im- 

 peccable maps published by government surveys . . . The geologist who fails to 

 distinguish fact from inference on his maps is inconsiderate both of other work- 

 ers and of his own reputation. As successors cannot tell wliich localities sup- 

 plied the evidence, they must search the whole area for exposed contacts. They 

 must either accept all of the work, fact and theory alike, or reject it all and start 

 the mapping from scratch . . . Thus the map should be drawn in such a manner 

 that either the man who made it or some one else will later be able to eliminate 

 all the interpretation, preserve all the observations and build up an entirely new 

 interpretation on the same set of facts ... It is his (the geologist's) duty to 

 offer interpretations at every opportunity, for no one is in a better position to 

 draw inferences than the man who has made the maps and studied the ground. 

 It is not speculation or imagination that is to be discouraged; it is merely the 

 failure to recognize and to indicate the element of uncertainty, a failure which 

 carries no.t only mechanical but also psychological dangers. The misconception 

 that one's theoretical interpretation is the only one possible is likely to be ex- 

 posed by the propensity of nature to contrive an interpretation that the geolo- 

 gist had not foreseen. 



6. Any portion or portions of an area that has been examined by a geolo- 

 gist is accounted for even though there are no outcrop exposures avail- 

 able for mapping. A good working theory of mapping is to account 

 for all area which has been examined in the field by posting some 

 symbol or color representing the mapped portion on the note sheet. 

 If the area is covered by soil, a symbol representing soil cover is posted 



' McKinstry, Hugh E.. Mining Geology, Prentice- Hall, p. 1, 1948. 



