NIAGARA AND LOWER HELDERBERG GROUPS. 119 



Perry and Decatur, on the Tennessee river, outcropping over 

 a wide area and affording numerous species of fossils in a fine 

 state of preservation. The base of the group here consists of 

 reddish and mottled limestones, very similar to those in 

 southern Illinois, and contain Ortlioceras undulatum, and 

 joints of large crinoids in great abundance. These red lime- 

 stones are succeeded by a series of greenish-gray shales, and 

 shaly argillaceous limestones, containing Caryocrinus orna- 

 tus, Calymene Blumenbachii, SpTicerexochus mirus, Platy- 

 ceras JYiagarense, Pentamerus oblongics, Orthis hybrida, 0. 

 elegantula, etc., associated with such Lower Helderberg forms 

 as Pentamerus galeatus, Spirifer perlamellosus, 8. macro- 

 pleura, Merista Iwvis, Rhynchonella ventricosus, and many 

 others, showing that the fossils of these so-called groups are 

 here intermingled through the same strata, confirming what 

 we had already assumed to be true in Illinois, that the Upper 

 Silurian beds of the west constitute but a single group, and, 

 consequently, that the term ' Lower Helderberg,' as applied 

 to a group distinct from the Niagara, is superfluous. We 

 recollect that, on visiting the locality of these so-called Lower 

 Helderberg limestones in the Schoharie valley some years ago, 

 we observed these limestones resting immediately upon undis- 

 puted Lower Silurian beds there, and, in explanation of their 

 occurrence in this apparent abnormal position, we were told 

 that the Niagara group was supposed to have thinned out to 

 the eastward, and that these Lower Helderberg limestones 

 took their place. But is it not quite as probable that there 

 has only been a change in the lithological character of the 

 beds in their eastern extension in New York, resulting there, 

 as in Illinois, in a decided change in the specific character of 

 the fossils which they contain, and that the Upper Silurian 

 beds at Schoharie are the exact equivalents of the Niagara 

 shales and limestones in the western part of the State? 



" To recapitulate, then, the facts as they are presented in 

 the west ; we find that the dolomites of northern Illinois con- 

 tain only Niagara fossils, and the silicious limestones of the 

 southern portion of the State contain only those considered 

 characteristic of the Lower Helderberg group ; while the beds 

 in Tennessee, occupying the same stratigraphical position with 

 the dolomites and the silicious limestones of Illinois, have 

 Niagara and Lower Helderberg fossils intermingled indiscrim- 

 inately through the strata. Hence we conclude that the so- 

 called Lower Helderberg group has no real existence as a dis- 

 tinct group of Upper Silurian strata, and that the name, being 

 superfluous, should be dropped from the nomenclature of the 

 American rocks." 



It is here proposed, in an article of less than three pages, tc 

 discard entirely from the geological series and geological 



