and South Central Pennsylvania. 407 



Arbuckle Mountain section. Comparing with this the Mohawk 

 Eiver section, 250 miles to the north, we find a striking discrep- 

 ancy. In the Mohawk section less than 500 feet of Beekman- 

 town rest with a basal conglomerate upon the Adirondack 

 gneisses, and is followed after an erosion interval by at the most 

 30 feet of Lowville (Upper Stones River or Upper Chazy). 

 This is conformably succeeded by the Black River and Trenton 

 limestones, ' ' 



In 1910 Ulrich (7) discusses the Lower Ordovician 

 (Canadian) limestones and dolomites of the Belief onte 

 section but writes nothing regarding the Middle Ordo- 

 vician series. In his correlation tables (op. cit., p. 27) he 

 lists the following formations: — Trenton (Reedsville; 

 Lower Trenton). Black River (Amsterdam; Lowville). 

 Stones River (Pamelia). 



In an "Outline of Practicum Work in General Geol- 

 ogy," which Prof. E. S. Moore has privately printed for 

 his class in Geology at Pennsylvania State College, the 

 Middle Ordovician is divided in the following manner : 



"Trenton, highly fossiliferous thin-bedded limestone and 

 black to brown shale, 791 feet. Black River : This group 

 includes the Black River and Lowville limestones which are usu- 

 ally pure, blue to grey rocks. The Lowville contains the famous 

 quarry-rock, 182 feet. Stones River, bluish limestone, 260 feet. ' ' 



A still more recent paper is that by Professor Ray- 

 mond (8) in which he says: 



"At Belief onte, Penn. according to the observations made by 

 Mr. Richard M. Field and the writer,, a zone of dark limestone, 

 containing such typical Leray (Black River) species as Colum- 

 naria halli( ?) and Maclurites logani, is followed by more argilla- 

 ceous limestone containing Echinosphcerites and a large number 

 of other fossils. Christiania has not yet been found in the 

 Bellefonte section, but this section does definitely show that the 

 Echinosphcerites zone is there younger than the Leray-Black 

 River of New York. As shown by Mr. Field, there is essential 

 agreement between the section at Bellefonte and that at Cham- 

 bersburg and Strasburg, so that all three of these occurrences of 

 Echinosphserites may be dated definitely as post-Leray." 



The preceding were the latest data which had been 

 published on the Middle Ordovician of central Pennsyl- 

 vania at the time that the writer finished his field work 

 in this region. The Bellefonte section has, however, 

 been visited by many geologists and paleontologists, in- 

 cluding members of the state and federal surveys, and 



