*ob PALEOZOIC TIME — DEVONIAN AGE. 



3. Articulates. — (a,) Crustaceans.— The Trilobites Phacops Bufo (fig: 

 499) and Dalmania calliteles (fig. 500, representing the posterior extremity) are 

 common in the Hamilton beds. 



Figs. 498-500. 



Cephalopod.— Fig. 498, Goniatites Marcellensis, Trilobites.— Fig. 499, Phacops Bufo; 500, 

 Caudal extremity of Dalmania calliteles. 



(b.) Remains of Insects have been found in the Devonian beds of St. John, New 

 Brunswick, which are either of the Hamilton or Chemung period. 



General Observations. 



Geography. — The positions and nature of the Hamilton beds 

 indicate similar geographical conditions to those of many earlier pe- 

 riods, — that a shallow sea covered New York and spread widely to 

 the west, and that many changes were experienced in the water-level ; 

 the beds are to a great extent mud-beds, whence we learn that 

 they were deposited in quiet waters ; the fossils are marine, proving 

 marine waters. The beds in New York are thickest about its cen- 

 tral parts, and yet spread to its eastern and western limits, ex- 

 cepting the Upper, the Genesee shale, which is not known in the 

 eastern part ; they are partly calcareous in the lower part of the 

 Marcellus beds, proving that the change from the condition of the 

 limestone-making Corniferous period was gradual ; limestone layers 

 occur higher up, at intervals, indicating changes of level, which 

 favored at times Encrinites and corals ; ripple-marked flags make 

 up some layers, proving by their evenness and extent, and the 

 regularity of the lamination, that the sea at the time of their forma- 

 tion swept over extensive sand-flats, coming in over the present 

 region of the Hudson River or of New York Bay. The existence 

 of a barrier of sand along the ocean, such as is thrown up and at 

 intervals removed again by the waves, would account for the vary- 



