VIEWS OF OTHER WRITERS 243 



One of the chief reasons for these varying views lies in the fact that 

 the lower limit of the Devonic of England has never been defined, and 

 its lowest well marked fauna is apparently not older than the Oriskany. 

 Again, Barrande included his Stages F, G, and H, together with the 

 Lower and Upper Helderberg, in the Siluric. These are now regarded 

 by most continental paleontologists, however, as of Lower and Middle 

 Devonic age. Americans have not apparently paid much attention to 

 the recent developments in the Lower Devonic of the Rhineland. Geikie 

 writes that — 



" It is rather from the sections and fossil collections of central Europe than from 

 those of England that the stratigraphy and paleontology of the Devonian system 

 are to be determined." 



Murchison, in reviewing his work of 1842 in the Rhenish area, twelve 

 years later, says : 



" 1 have been convinced, through the paleontological labors of Ferdinand Roemer 

 and the brothers Sandberger, that the types of that lower Rhenish subdivision are 

 distinct from the Upper Silurian, and in harmony with the lowest Devonian group 

 of other countries." 



The geographically restricted condition of the Lower Helderberg and 

 the completeness with which its fauna was described by Hall, in 1859, 

 have left Americans little opportunity to examine its systemic position. 

 The influence of that great nestor of American geologists has so estab- 

 lished the position of the Lower Helderberg, that writers of text-books 

 seem unwilling to set aside his conclusions. When Clarke published 

 his paper on " The Herc3?nian question " the present writer was assist- 

 ant to Professor Hall. At that time, Clarke proved the unmistakable 

 Devonian aspect of the Low T er Helderberg fauna, and Hall is not known 

 to have objected to this presentation. Walcott,* in reviewing Clarke's 

 paper, states in conclusion that — 



"This suggestion [Lower Helderberg = Lower Devonian], comes to me with 

 peculiar force at the present time, and, if the Silurian system was to be reclassified 

 today, I should favor the following scheme : Lower division, Canadian, Calciferous, 

 and Chazy ; middle division, Trenton and Hudson, and upper division, Niagara 

 and Salina. The summit of the Silurian would be drawn at the Waterlime forma- 

 tion, and the Lower Helderberg would be considered, with the Oriskany sandstone, 

 as lowest Devonian. This, to my mind, is the more natural classification, and 

 divides the Paleozoic into four subequal groups— Cambrian, Silurian, Devonian, 

 and Carboniferous." 



It may be well to state here that most system boundaries are estab- 

 lished in regions where some physical event has made a break in the 



*Amer. Jour. Sci., vol. xxxix, 1890, p. 156. 



