COMPOUND EEGRESSIVE AND TRANSGRESSIVE OVERLAP 



619 



break included within the Saint Peter sandstone of Minnesota is equiva- 

 lent to the upper thousand feet of the Arbuckle plus the lower 1,900 feet 

 or more of the Simpson formations, since this latter formation is followed 

 by beds with a Black Eiver fauna (lower Viola limestone). These rela- 

 tionships are graphically shown in the following diagram: 



Figure 9. — Relationship of the Arbuckle and Simpson and the Stones River and Mag- 

 nesian Formations, and position of the Saint Peter Sandstone. 



In the Nittany valley of Pennsylvania* (Center county) the Beekman- 

 town consists of nearly 2,500 feet of limestones, sometimes brecciated, 

 often dolomitic and with siliceous sands at the base. Ophileta complanata 

 occurs about 200 feet above the exposed base, but the lowest beds are not 

 shown in this section. Toward the middle occurs Asaphus marginalis 

 and Ribeiria calcifera, and toward the top of the series Bathyurus ampli- 

 marginatus, Maclurea affinis, Liospira strigata, Protowartliia rossi, and 

 Dalmanella subcequata gibbosa. This fauna, as remarked by Collie, is an 

 Upper Beekmantown fauna. 



The fossiliferous beds are succeeded by 2,335 feet of ". . . com- 

 pact yellowish gray and drab dolomitic limestone frequently thin bedded 

 and laminated, alternating with numerous thin beds of dark limestone, 

 weathering to a light gray color. Nodules of chert occur frequently, and 

 in such occurrence the rock tends to be arenaceous." This is also referred 

 to the Beekmantown by Collie, but may be of later age. It is followed 

 by 235 feet of carbonaceous crystalline black limestone alternating with 

 gray limestone and containing Leperditia fabulites, Protorhynchula 

 ridleyana, and other fossils of Upper Stones Eiver age. Succeeding this 

 are 93 feet of Black Eiver and 603 feet of Trenton limestone. 



Since the fossiliferous horizon below the 2,335 feet of unf ossif- 

 erous ( ?) beds is upper Beekmantown and the first fossiliferous horizon 

 is Upper Stones Eiver (Upper Chazy), the lower Stones Eiver, or Chazy 

 proper, seems to be represented by this unfossiliferous ( ?) horizon. If, 

 then, this series is taken from the Beekmantown and added to the Chazy, 

 we have 2,500 feet — of the former and 2,500 feet ( + ) of the latter, a 



* George L. Collie : Ordovician system near Bellefonte, Pennsylvania. 

 Am., vol. 14, pp. 407-420. 



Bull. Geol. Soc. 



