58 AMADEUS W. GRABAU 



term Canadian becomes obsolete. The Beekmantownian corresponds 

 essentially to the Arenigian of England and its continental equivalent. 



B. THE MIDDLE ORDOVICIC OR CHAZYAN 



In its maximum development, the Chazy shows nearly 2,500 feet 

 of limestones, many portions of which are highly fossiliferous. An 

 apparently complete development of this series, resting with con- 

 formity upon the Beekmantown, is described by ColHe from Center 

 County, Pennsylvania. Here 2,335 ^^^t of dolomitic limestones, 

 with fossils poorly preserved, succeeds the Upper Beekmantownian; 

 and above this is 235 feet of fossiliferous limestones of Upper Stones 

 River (Upper Chazy) age, succeeded in turn by the Black River. 

 Sedimentation seems to have been continuous throughout, and this 

 section may therefore be regarded as typical of the Mid-Ordovicic 

 in its entirety. In southern Pennsylvania, Stose reports a discon- 

 formity and hiatus between the Beekmantown and Chazy (Stones 

 River) limestones. The latter are from 800 to 1,000 feet thick, and 

 are succeeded by the Chambersburg limestone (100 to 600 feet thick), 

 which carries an Upper Chazy and Black River fauna. Continuous 

 deposition seems to have obtained between the tw^o series. In the 

 Lake Champlain region, a hiatus also exists between the Beekman- 

 town and Chazy, with the result that only about 900 feet of Chazy 

 occurs in this region below the Black River beds. In western New- 

 foundland at least 2,000 feet of strata is referable to this series, the 

 succession being conformable. Here, however, the upper limit of 

 the Chazy is not known, the highest bed (P) being succeeded by 

 continental sediments of much later age. 



In the Arbuckle Mountains the hiatus between Beekmantown and 

 Chazy is marked by a sandstone, and only the upper 2,000 feet of 

 the Chazy (Simpson) is shown, followed by Black River. The 

 Chazy is absent in the Mohawk Valley, except for a few feet of 

 LowvilJe which lies disconformably upon the eroded surface of the 

 Lower Beekmantown (Little Falls dolomite), and is conformably 

 succeeded by the Black River. In the Black River Valley, at Water- 

 town and northward, the sedimentation from Lowville to Black River 

 is continuous and gradual. Cushing' finds in the Theresa quadrangle 



I Bull. Geol. Soc. Amer., Vol. XIX, pp. 155-76. 



