12 J. D. DANA — A.REAS OF CONTINENTAL PROGRESS. 



down by me in 1875, the Appalachian area corresponds to the Eastern 

 Interior. Prof. II. S. Williams, in his communication on the Devonian in 

 lss7 to the committee of the International Geological Congress, recognized 

 the t'aet that the term Appalachian and my definition of it gave it too narrow 



limits ami used that of Eastern Interior. 



The Central Interior might be further divided into an East-Central and 

 West-Central, along a line commencing in the chief Archaean region of Mis- 

 souri, an island, or group of islands, in the Paleozoic sea, to the west of which 

 the Upper Silurian and Devonian strata appear for a long, undetermined 

 distance to be mostly or wholly wanting. 



The title of my paper includes, as its second clause, " the influence of the 

 conditions of these ana- on the work carried on within them." I will now 

 illustrate this point by going into some detail with regard to one of these 

 sections, the Eastern Interior. 



The influence of the Cincinnati harrier on subsequent rock-making has 

 been recognized by Professor Hall, Professor Newberry, and others, but I 

 think that this influence was much greater than has been appreciated. Note 

 the position and length of this partial harrier of shallow seas and emerged 

 lands between the Western and Central Interior, its extension from Lake 

 Erie, or the southeast side of Lake Huron to Southern Tennessee and some- 

 what beyond it, and then consider the size of the area enclosed, namely, 

 parts of Mississippi, Alabama, and Eastern Tennessee, Eastern Kentucky, 

 West Virginia, Eastern Ohio, nearly all of Pennsylvania, ami all of New 

 York, excepl it- northern portion, the length not less than TOO miles. Note 

 also that the great subsiding Appalachian trough, or group of troughs, ex- 

 tended over a broad eastern portion of the area, ami that the subsidence 

 involved to some extent the whole. 



Now, when the Upper Silurian era opened, the region of Albany in 

 Eastern New York was near the head of a great Northeast Bay in this 

 Eastern Interior Sea. It was essentially a hay ; for the old sea-channel of 

 the Lower Silurian era, extending over the Lake Champlain region to 

 Canada, in which the Lower Silurian formations had in succession been laid 

 down, was closed by the beginning of the Upper Silurian, :i- the records of 

 the Niagara period show, or, at [east, so far closed as to he no longei a con- 

 tributor toward rock-m iking, and it e mtinued to be thus far closed except 

 during the Lower Helderberg period, through the resl of Paleozoic tim< 



* The closing of the i I nol have 1 lete through all this time as to have ex- 



ejudi termigration ■ i- probable thai the chief open paw i ird !"■ 



Ivsnia where the Arch 

 protaxii has i minimum height The waters over tnis wide connecting 



kve left vi l.'M s of the Upper Silurian, Deronl 



. in 1 1 i in- they would nol )"• likely to •!" unless 1 1 • • - region 

 eg) •!> of i would I i . Vfiy thin and easily 



washed awav. 



