172 Forty-sixth Report on the State Museum, 



America and the explorations of Columbus, and of the early voy- 

 agers who followed him. These maps have gradually become 

 more and more unreliable with progress of time ; but it is only in 

 modern times that we have had maps constructed upon careful 

 and reliable surveys, this being equally true of geographical and 

 geological maps. It can not be expected that early efforts in 

 producing geological maps will be more accurate than the geo- 

 graphical maps on which the data were recorded. It is not neces- 

 sary to make an apolog}^ for this state of things; it is an absolutely 

 necessary condition, and the geologists of today who criticise the 

 efforts presented on geological maps of half a century ago, should 

 remember that only a small part of our country has yet been sur- 

 veyed with sufficient accuracy to record the geological data with 

 a degree of exactness which will enable them to withstand the 

 investigations of the next qaarter of a century. 



The fundamental topographical as well as the geographical 

 features of the country may be represented in a general way 

 upon the ordinary geographical map, and it is only when we 

 attempt to carry this representation of geological features into 

 detail and to note the minor subdivisions of those rocks which 

 form the salient features of the country that we find the necessity 

 of more accurate geographical maps. In the prevailing activity 

 among scientific men, it is not prudent for any man to represent 

 the limits of geological formations otherwise than from the most 

 careful and critical investigations, leaving untouched and uncolored 

 those portions of country he has not examined, or which cannot 

 be examined with present means, or under existing conditions. 

 Both in geography and geology the temptation always comes to 

 extend the area of our knowledge beyond that which we have 

 actually determined by carefully traversing the country. Both 

 the geographer and the geologist labor under the same difficulties 

 and temptations ; each one fearing to leave unrepresented and 

 uncolored any portion of country which he has even but cur- 

 sorily examined. In the present condition of industrial knowledge, 

 where each rock formation may have an economic value, the pres- 

 entation of a geological map to the public incurs grave responsi- 

 bilities, and it will be far better to leave uncolored those 

 portions which can not be satisfactorily represented, than 

 to color in its entirety any map of a state or a portion of a state 



