PiaBBUAET 26, 1909] 



SCIENCE 



355 



cepting the former equivalency, the dividing 

 line between Middle and Upper Ordovicic 

 should be drawn at the summit of the Black 

 River. This is where Freeh draws it, throw- 

 ing the Trenton limestone into the Upper 

 Ordovicic. In this I believe he is correct, 

 though I am not fully prepared to class the 

 Black Eiver with the lower horizon. Dana's 

 tentative correlation of American and British 

 Ordovicic strata parallels Arenig and Beek- 

 mantown, Llandeilo and Chazy, Bala-Caradoc 

 and Trenton, and the lower Llandovery and 

 Utiea-Hudson. The lower Llandovery is now 

 referred to the base of the Siluric ; the " Hud- 

 son " (Lorraine-Eichmond) together with the 

 Utica-Trenton thus being referable to the 

 Caradocian. 



For the American Middle Ordovicic the 

 term Chazyan is here proposed. The old term 

 Canadian would as a result become of no 

 further significance. For the Upper Ordovicic 

 the term Trentonian may serve, since Trenton 

 deposition covers at least one half this divi- 

 sion. Moreover, the name Trenton Period 

 was used by Dana for Trenton limestone and 

 later divisions. Nashvillean would perhaps 

 be a better name, if it is a fact that the Nash- 

 ville group of Safford covers both Trenton and 

 later Ordovicic formations. Cincinnaiian is 

 definitely in use for Eden to Richmond inclu- 

 sive, and though its meaning might be ex- 

 tended to include Trenton limestone, the fact 

 that it is in general use for the higher beds 

 might lead to confusion. The term Mo- 

 hawkian would, of course, fall into disuse. 



In the Appalachian region, extensive fans 

 of continental deposits were formed during 

 late Ordovicic and early Siluric time." In 

 southern Pennsylvania these comprise the 

 basal white beds, generally referred to in the 

 literature as " Oneida," and for which the 

 name Tyrone is proposed, from a locality in 

 Pennsylvania where they are typically shown; 

 the middle red beds or Juniata, often called 

 red Medina ; and the upper white or Tuscarora, 

 commonly called white Medina. (The Green 

 Pond conglomerates and Longwood shales, 



° These will be fully discussed in a forthcoming 

 paper by the author. 



and their equivalents in the Delaware and 

 Schuylkill gaps, are not referred to here. 

 They belong in the Salina or Middle Siluric 

 division.) In western New York, the Juniata 

 is represented by the Queenston shales of the 

 present author (red Medina shales of most 

 authors), and the Tuscarora in part by 

 Medina. The Siluro-Ordovicic dividing line 

 falls approximately between these two, i. e., 

 between the Juniata and Tuscarora, or the 

 Bays and Clinch, their southern equivalents. 

 Fossils in the Juniata and Bays (included 

 where the river-laid beds dipped into the sea) 

 indicate their late Ordovicic (Upper Lorraine) 

 age. 



The Siluric has been discussed in a previous 

 communication (January 6, 1908, Science, 

 N. S., Vol. XXVn., pp. 622-23, April 17, 

 1908), and wiU be more fully treated in the 

 forthcoming article already referred to. The 

 essential points to be noted are : (1) That the 

 Oswegan of Clarke and Schuchert is now 

 known to be in part Ordovicic and in part 

 Salinan. (2) That the Siluric begins with 

 the Medina sandstone (exclusive of Queens- 

 ton shales) of western New Tork, which has 

 a thickness of about 100 feet (Upper Medina 

 of authors generally) and contains a fairly 

 abundant fauna of Siluric age, most nearly 

 related to the Clinton. (3) That the Clinton 

 of the type section in eastern New Tork in- 

 cludes apparently part of the higher Niagaran 

 beds of western New Tork. (4) That the pre- 

 " Clinton " Siluric beds of the interior (Cape 

 Girardeau beds; Alexandrian beds of T. E. 

 Savage) are to be classed with the Lower 

 Siluric, for which the term Niagaran, used 

 by Dana for all these, is to be restored. (5) 

 That the Middle Siluric is represented only in 

 the interior of North America by the non- 

 marine Salina, including the Green Pond- 

 Shawangunk and Longwood beds. (6) That 

 the Monroe formation or Monroan of Mich- 

 igan, Ohio and Canada constitutes the true 

 Upper Siluric, the Cayugan of New Tork 

 (exclusive of the Salina) representing only 

 the uppermost portion of the Monroe series. 



Expressed in tabular form, the classifica- 

 tions here proposed are as follows : 



