MIDDLE AND UPPER ORDOVICIAN. 187 



Beekmantown, by an unconformity, while it invariably grades into tbe Potsdam beneath 

 through a series of passage beds ; and that f aunally also its association is with the Potsdam, the 

 Hoyt limestone of the Saratogan region being merely a more calcareous and more fossUiferous 

 phase of its lower portion, of very local character, rather than a phase of the Potsdam. 



Local sections of the Ordovician in the Mohawk Valley have been described 

 with great detail and faunal lists are given in publications by Cumings,"' Cushing,^"^ 

 Prosser,""' ''' Walcott,«« and White.'"'- »"'' ''° 



The Champlain-Hudson Valley is here mapped according to the authorities 

 cited by Merrill ^'^* for Clinton, Washington, Rensselaer, Columbia, Dutchess, Ulster, 

 and Orange counties. The Ordovician of this region comprises, above the Beek- 

 mantown, the Chazy, Trenton, and "Hudson River." The Chazy is restricted to 

 the northeastern section. '^^ Near Albany the "Hudson River shales" are now 

 recognized as representing, in ascending order, the Normans Kill, middle Trenton, 

 Utica, and Lorraine. The Normans Kill shale is a clastic representative of the 

 lower Trenton limestone of the western part of the State. 



It is convenient to take up the discussion at the north in Clinton County and 

 to proceed southward. Cushing's general statement of the relations of the several 

 Ordovician formations around the Adirondacks is quoted on page 186. The Chazy 

 is thus described by Cushing : ^"^ 



Brainard and Seely have recognized three subdivisions of the Chazy rocks. * * * xhe 

 lower subdivision is largely constituted of quite crystalhne limestones of gray color, often full 

 of crinoidal fragments and with Orihis costdlis the most abundant fossil; the naiddle division 

 is of blue-black fine-grained limestone and contains Maclurea magna at nearly all horizons ; the 

 upper division is quite variable in character but is largely composed of somewhat impure blue 

 limestones, carrying Khynchonella plena abundantly. 



The aggregate thickness of the Chazy limestone at Chazy village is 740 feet, with the base 

 not shown. On Valcour Island, Brainard and Seely give it a thickness of 890 feet, and there it 

 seems to reach its maximum." 



Brainard's section at Valcour Island *•* reads, in ascending order: 



Group A (Lower Chazy) . 



1. Gray or drab-colored sandstone, interstratified with thin (or sotaetimes thick) layers of slate, 



and with occasional thin layers of limestone at the base, containing Camerella (?) costata Feet. 

 Bill 56 



The slaty sandstone gradually passes into — 



2. Massive beds, made up of thin alternating layers of tough slate and of nodular limestone, 



containing undetermined species of Orthis and Orthoceras 82 



3. Dark bluish-gray, somewhat impure limestone, in beds of variable thickness; often packed 



with Orthis costalis Hall, which occurs with more or less frequency through the whole 

 mass. Other fossils are Lingula huronensis Bill., Harpes antiquatus Bill., Harpes otta- 

 waensis Bill. ( ?) , Illxnus arcturus Hall ( = bayfieldii Bill . ) , Lituites sp . (?) 110 



4. Gray, tolerably pure limestone in beds 8 to 20 inches thick, separated by earthy seams, the 



bedding being uneven. Many layers consist of crinoidal fragments, largely of Palieocys- 

 tites tenwiradiatus Hall. Near the middle of the mass, for a thickness of 10 feet, some of 

 the fragments and small ovoid masses {Bolhoporites americarms Bill.) are of a bright-red 

 color, and these beds on the west side of Bluff Point are extensively quarried and furnish 

 a fine marble for indoor use 90 



Total thickness of A 338 



o Ulrich regards this as a mistake, for in his judgment it robs the Beekmantown of its most essential part, namely, 

 division D. — B, W. 



