walcott.] CORRELATION. 399 



Lyell, Mantell, and various French and German authors. Their influence 

 is shown by the rapid development of stratigraphic geology based upon 

 the principles established in Europe. Of the means of correlation avail- 

 able to Prof. Amos Eaton in his earlier work he says, in 1839 : 



Eaton. — When I commenced my geological surveys the application of organized 

 remains for demonstrating strata was not studied in America. I had become ac- 

 quainted with no method for determining the character of such strata but that of 

 tracing them separately through a vast extent of country and then comparing their 

 general characters. For this purpose I traveled some thousand miles at my own ex- 

 pense a'nd with the liberal aid of students of Williams College, with Prof. Dewey at 

 their head, where I was employed more than a score of years since by the authorities 

 of the college to introduce the natural sciences. Afterwards I traveled more than 

 17,000 miles on geologizing tours at the expense of the Hon. Stephen Van Rensslacr, 

 and I was always aided by several assistants and competent students. Had the ap- 

 plication of paleontology been then as well understood as it now is I could have 

 settled the characters of most rocks as well in my closet by the aid of specimens. 

 But it is a true remark in your last journal that strata must have been first settled 

 according to the method to which I was compelled by ignorance to submit, before 

 the service of organized remains could be successfully employed. In this country no 

 material progress had then been made in the study of organized relics, and even now 

 we have very few good paleontologists. 1 



NEW YORK SURVEY. 



The geologists of the New York State survey systematized the work 

 of the geologists who preceded them and established a standard section 

 of the lower and middle Paleozoic formations of New York. On this 

 account it is desirable to examine the principles of correlation men- 

 tioned by Messrs. Conrad, Hall, and Emmons and to notice the extensiou 

 of the nomenclature of the formations of the New York section to vari- 

 ous portions of the continent. 



Conrad. — As paleontologist of the survey Mr. T. A. Conrad made the 

 following comments upon the use of fossils in the correlation of strata : 2 



There is a strange misunderstanding of the method of applying organic remains 

 in the division of series of strata into formations and the identification of widely 

 separated rocks by the zoological characters of each. In the January number of the 

 New York Review the opinion is advanced that the "Calyniene blumenbachii ought 

 to be carefully sought for in the rocks which are said to correspond to the Dudley 

 jperiod. Unless it is found, or some other consideration is introduced, can it be be- 

 lieved that fossils are a satisfactory evidence of the age and place of rocks?" The 

 line of demarcation between rocks of different age has never yet been drawn with 

 any accuracy by the aid of paleontology, except by the consideration of groups of 

 species, one or even a few species having no weight whatever in the determination. 

 Thus the shell termed Terebratula Schlotheimii dates its existence with the Trenton 

 limestone, and reappears in three of the latter formations of the Silurian system. Or- 

 th%8 t€8tudinaria, Dalrn., is peculiarly characteristic of the Trenton limestone, by its 

 almost invariable presence and extreme abundance, and yet it is also found in the 

 limestone of the Helderberg, a formation of a far more recent origin. But, although 

 a few species may have been continued through a succession of geological eras, the 



1 Cherty limerock or Corniferous limerock, proposed as the line of reference for State geologists 

 of New York and Pennsylvania. A m. Jour. Sci., vol. 36, 1839, p. 67. 



*Second annual report of the paleontological department of the survey. Third annual report of the 

 geological survey of New York, 1839, p. 58. Albany. 



