OUTLINE OF THIS PAPER. 



The following essay is a historical study of the classifications and nomenclatures 

 of geological formations in America, made with the purpose of ascertaining how 

 satisfactory correlations have been made and upon what principles they have been 

 based. For this purpose the literature upon the whole Paleozoic for the first 40 

 years of the century has been reviewed, but for the period following the publication 

 of the Final Reports on the Geology of the State of New York (1842-1844), the study 

 has been confined to the literature of the Devonian and Carboniferous systems. 



In the course of the historical development of the science, and as the geological 

 surveys have extended over new territory, a number of specific problems have arisen 

 for the solution of which it has been necessary to determine the relations between 

 standard formations already •named and classified and those newly discovered. In 

 this essay the discussion of each of these problems has been followed out in detail, 

 the various attempts at correlation have been noted, and the methods employed and 

 the final results attained have been traced to the principles involved in their deter- 

 mination. 



The following problems have been thus discussed : 



(1) The general correlation of the Paleozoic formations of eastern North America 

 with the corresponding formations of Europe. 



(2) The determination of the parallelism between the upper Paleozoic formations 

 of the Appalachian region and the rocks of the interior of the continent as far west 

 as the Mississippi River. 



(3) The correlation in the Northern Appalachian region of the various subdivis- 

 ions of the Coal Measures and formations immediately underlying them. 



(4) The problems connected with the correlation of the Chemung and Catskill 

 groups, and with the correlation of the Waverly and Marshall groups. 



(5) The elaboration of the Mississippian series, or "Subcarboniferous" formations 

 of the Mississippi River basin. 



(6) The Permian problem of Kansas and Nebraska. 



(7) The correlation problems involved in classifying (a) the formations of the Aca- 

 dian province, and (6) the formations of the Rocky Mountains and Western Plateau 

 provinces. 



In the discussion of these various problems several definite stages in the develop- 

 ment of the principles of correlation have been recognized. At the opening of the 

 century the Wernerian system of classification was generally adopted. In this 

 classification the mineral characters of the formations were regarded as of funda- 

 mental importance, and constituted the chief criteria for their classification and cor- 

 relation, and the order of deposition was supposed to be indicated by the actual and 

 relative position of the present outcropping of the strata. The theory underlying 

 this latter interpretation was, that the older rocks formed the core of the mountains; 

 on the higher part and at an inclination were formed the next younger, and as the 

 waters dried off the surface of the earth the successive rocks were deposited at lower 

 and lower levels. The names " Primary," " Secondary," " Tertiary," and "Quater- 

 nary " preserve the memory of this theory, though the theory itself has given way to 

 the more rational one of oscillation of the crust of the earth itself, with relative sta- 

 ll 



! 



