PHYSICAL AND FAUNAL EVOLUTION 223 
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 Collie from Center 
County, Pennsylvania. Here 2,335 feet 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 two series. In the 
Lake Champlain region, a hiatus also exists between the Beekman- 
town and Chazy, with the result that only about goo 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 
Lowville 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 
t Bull. Geol. Soc. Amer., Vol. XIX, pp. 155-76. 
