10 .1. D. DANA — AREAS "I CONTINENTAL PROGRESS 



schists are Lower Silurian, as has I a suggested by several writers on the 



region. 



&for< >ver, the protaxial area, thus widened, was probably, throughout later 

 Paleozoic time, an emerged area to the south as well as to the north — that 

 is, it was above the level of marine waters. Great subsidence took place 

 over the Triassic areas of the Atlantic Border region — 2,000 to 5,000 feet 

 at least — but it took place without letting in salt water. They were local 

 subsiding areas or troughs. 



The same widening of Archaean boundary-ranges by an inclusion of Cam- 

 brian and Lower Silurian areas probably took place, also, in New Bruns- 

 wick and Nova Scotia. 



Fourthly. These facta from Eastern America with regard to the break he- 

 tween the Lower and Upper Silurian make it apparent, and more so than has 

 been hitherto recognized, that the close of the Lower Silurian era marks offone 

 of the grander divisions in American geological tim >, asii does also, though l< 

 strikingly, in that of Europe. The importance of the epoch in geologi- 

 cal history is manifest also in Western America; for while evidence of any 

 disturbance fails, the Upper Silurian is to a large extent absenl or nearly 



if we may judge from known facts. Consequently, the boundary lines 

 of the Lower Silurian areas, not unfrequently omitted, are among the most 

 importanl of the lines which a geological map of North America, or of the 

 World, should contain. 



1 take this opportunity to add, as a second corollary, that then is good 

 reason in the importance of the Lower Silurian era— g 1 chronological, geo- 

 logical, and paleontological reason — why the name Silurian, which the Lower 

 Silurian has so long held, should be perpetuated to it, and good reason why 

 the name should not become attached only to the small end of the Silurian 

 era, the so-called U pper Silurian, which has little in its new type- that is 

 nol more characteristically Devonian, and which bas do! one-fourth the area 

 of distribution or thickness of strata in North America that the I. own- 

 Silurian has. There is reason for this also in what is due to the came of 

 Murchison, whose labors for his " Siluria " where largely among the Lower 

 Silurian rocks, and who.-e troubles with Sedgwick cameoul of their separate 

 labors in Lower Silurian and < lambrian rocks without the intention in either 

 of encroaching on the other's rights. 



The Upper Silurian may conveniently take a new name, hut it is ool 

 me. ssary to go for it to the aame little land of Wales that has supplied the 

 two, Cambrian and Silurian, in honor of Sedgwiok ami Murchison. \\ • 

 may better look elsewhere for the third name. There is the land of Bohemia, 

 where Barrande worked oul his Silurian and Primordial systems, and tin re 

 is the area of V-w York and Canada where were laid the foundations of 

 American Paleozoic geology, and where our honored president, James Mall, 

 has carried on his paleontological labors. 



