250 C. BCHUCHERT — LOWER HELDERBERG-ORISKANY FORMATIONS 



of life. It was rather that of the Niagara epoch, which continued to 

 live and undergo modification in some unknown area while the Salina 

 shales and Waterlimes were deposited. This fauna, transitional hetween 

 the Niagara and the Lower Ilelderherg, may he that of the Guelph, 

 Meniscus, and the higher Siluric dolomites of Ontario and the central 

 United States. In an}'' event, the Tentaculite fauna has a decided Siluric 

 facies. It seems that the most natural line (faunally) for the separation 

 of the Siluric and the Lower Helderherg lies at the top of the Tentaculite 

 limestone, and that the fauna of the Lower Pentamerus is the earliest 

 stage in the Devonic C}' , cle of marine life. 



Suhmergence and transgression begins with the Tentaculite, but in 

 the Lower Helderherg sea are more decided than during any period of 

 the Siluric. In eastern Pennsylvania the Lower Helderherg reposes on 

 Clinton strata ; in southern Illinois and adjoining Missouri, on Ordovicic 

 strata, and in Gaspe on the Quebec. This evidence, therefore, shows a 

 marked transgression over eroded land areas in widely separated local- 

 ities. The Oriskany sea continues the Lower Helderherg submergence 

 and transgression, since in New York, from east to west, it gradually 

 comes to rest on the various members of the Lower Helderherg and 

 finall}' upon the Waterlime (= Rondout limestone). 



In 1882, Hall * also pointed out that " while the trend [line of greatest 

 deposition] of the limestones of the Niagara and the two succeeding 

 calcareous groups has a general east and west direction, the Lower Hel- 

 derherg has a northeast and southwest trend." 



It may also be w T ell to state here that the Lower Helderherg is nearl} r 

 everywhere followed by some member of the Oriskan} T . This is true 

 for New York as well as practically throughout the length of the Appa- 

 lachians, Illinois, Tennessee, and Gaspe. The Oriskany is absent in 

 Indian Territory, and is present without the Lower Helderherg in the 

 region of Cayuga, Ontario. 



Mr Bailey Willis, of the United States Geological Survey, who has 

 made a special study of the middle and southern Appalachian moun- 

 tains, will publish the following in the third volume of the Geological 

 Survey of Maryland : 



"The student of physical changes finds no important episode of mountain 

 growth or continental development to define the close of the Silurian period and 

 the beginning of the Devonian. The record descrihes Appalachians a monotonous 

 lowland, now rising a little higher, now not so high, above the fluctuating coast 

 <>f marsh and tideflat. . . . Before the Oriskany in the Lower Helderherg 

 epoch it had assumed these aspects which are considered to characterize the 

 Devonian period." 



* Contribution to Geol. Hist. Amer. Cont. Presidential address, A. A. A. S. s Montreal, is">7. Re- 

 published, Salem, iss-2, pp. 48, 49, 68. 



