THE OROGENIC EPOCHS IN NORTH AMERICA 635 



them, and in the conscious discrimination between the crumplings 

 and disturbances of other kinds. For example, Lyell^ in 1855 makes 

 no specific mention of such events; Dana^ in 1875 enumerates seven 

 more or less distinct epochs; Leconte^ in 1891 gives four; Dana^again 

 in 1895, eight more fully detailed than in 1875 ; Chamberlin and Salis- 

 burys in 1905, six; Scott^ in 1907, five; and Haug'^ in 1910-11, four 

 (for North America). Dana was apparently among the first to see 

 clearly that there had been a succession of foldings separated by 

 periods of relative inactivity, and he early realized their importance 

 as milestones in the progress of the earth's history. If all writers 

 on the geology of local districts had even in recent years been as 

 careful as Dana to distinguish between folding and mere change of- 

 level, or between folding, faulting, and volcanic activity, it would 

 now be much easier for students of geologic history to interpret the 

 local reports which necessarily form the basis of such general 

 studies as this. We should not then be left in doubt as to just 

 what an author means by the phrase, ''a disturbance at the close of 

 the Eocene" or "saccular changes in Acadia"; nor would the 

 "Appalachian revolution" be described as extending from the close 

 of the Mississippian to the end of the Trias and affecting most of 

 North America. 



The following list (Table I) of orogenic epochs is compiled for 

 the use of students of geologic history without any pretense of 

 adding materially to the existing fund of knowledge upon the sub- 

 ject. Like codifications in general, it may serve quite as much to 

 call attention to the existing lack of knowledge on many points, as 

 to present what is already known. Each of the orogenic epochs 

 deserves to be the subject of a special investigation, for the purpose 

 of ascertaining more exactly the date and duration of the dis- 

 turbance, its relations to those in other continents, the special 



' Sir Charles Lyell, Elements of Geology, 5th ed. 



=^ J. D. Dana, Manual of Geology f 2d ed. 



3 Jos. Leconte, Elements of Geology, 3d ed. 



" Op. cit., 4th ed. 



s T. C. Chamberlin and R. D. Salisbury, Geology, Vols. II, III. 



^ W. B. Scott, Introduction to Geology, 2d ed. 



7 Emile Haug, Traite de Geologie, Vol. II. 



