FIFTH REPORT OF THE DIRECTOR I908 115 



ONE HUNDRED YEARS OF NEW YORK STATE 

 GEOLOGIC MAPS 1809-1909 



BY HENRY LEIGHTON 



In geology as in other sciences, no satisfactory understanding of 

 the subject can be acquired without a knowledge of the history of 

 its development. As Geikie says " it is eminently useful, now and 

 then, to pause in the race, and to look backward over the ground 

 that has been traversed, to mark the errors as well as the successes 

 of the journey." 



We have thought it of interest to review briefly the development 

 of geology in New York State as evidenced by the published maps, 

 and to publish a list of such maps arranged in chronological order 

 and indexed; this list not only to serve as a reference index to all 

 geological maps of the State but, as well, to show briefly the devel- 

 opment of the science of geology in the State. 



For the clear interpretation of the geology of a region, both in 

 the distribution and structural features of its rocks, geologic maps 

 are almost indispensable as an accompaniment to a written descrip- 

 tion. This fact was comprehended by the very early observers, and 

 even before geology as a science was recognized, geologic or, more 

 correctly, mineralogic maps were drawn. By all writers the credit 

 for the publication of the first map showing geological features has 

 been given to Jean Etienne Guettard who in 1751 1 issued a map 

 of Paris and its environs. This was more of a mineralogic than a 

 geologic map, its author seemingly having no conception of geologi- 

 cal structure or sequence of formations. Guettard, unlike many 

 scientists of his time and many more following him, was not of a 

 speculative turn of mind, but believed strongly in observation as 

 the best means of deriving important scientific truths. Originally 

 a botanist, in his botanical excursions he became interested in the 

 minerals and fossils he came across, and soon became convinced of 

 the fact that minerals and fossils were not promiscuously distributed 

 over and through the rocks but were arranged in definite bands. 



He then conceived the idea 2 of fixing his observations by the use 

 of a map showing the mineral and fossil localities, which were indi- 



1 Mem. Acad. Roy. Sciences, France. 1751. 



3 A similar plan, although probably unknown to Guettard, was proposed 

 in a paper presented before the Royal Society of London in 1683. 



