^0. 3.] AMERICAN ASSOCIATION. 161 



*overlie unconformably the disturbed Quebec group or Lower 



-Cambriam. These two great series correspond to tlie rocks of 

 the first and'secood faunas of Barrande. The second great break 



:is at the summit of the Hudson River group, and is marked by the 



■■Oneida conglomerate in New York, and a simihir one in Ohio, 

 •deseribed by Newberry, The rocks above, to the base of the 



Oorniferous limestone in the New York series, are the Upper 

 Silurian of Murchison, or Silurian proper, and hold what is call- 

 ^ed by Barrande the third fauna. As long since shown by Hall 

 :they are, however, to be divided on palaeontological grounds into 

 -two groups, the lower including the Medina, Clinton, and Niagara 

 formations, and the upper what was named the Lower Helder- 

 berg group. These are separated in New- York and Ontario by 

 .the great noB-fossiJliferous Onondaga group, holding salt and 

 gypsum, and deposited from a great mediterranean salt lake. 



" The close of the Onondaga was marked by another period of dis- 

 turbance which, like that preceding the deposition of the Tren- 

 ton, changed the levels and caused the ocean waters to spread 

 alike over the Onondaga formation and the adjacent rocks, which 

 had formed the ancient sea barrier. Then were deposited the 

 Lower Helderberg limestones, followed by the Oriskany sand- 

 stone, too'ether constituting a fourth natural division of our pa- 

 ^laeozoie rocks. These strata were deposited unconformably over 

 the Trenton and Hudson River rocks, in the St. Lawrence val- 

 ley, and in various localities among the Appalachian hills in New 

 Endand and the British Provinces. Over this whole reo;ion 

 there are no known representatives of the second, and, except to 

 the far eastward, none of the third, or Medina-Niagara fauna. 

 "The fourth or highest Silurian fauna corresponds to the Ludlow 

 rocks of Britain, or Upper Silurian of the Canada Survey ; while for 

 the third fauna they have applied the name of Middle Silurian. 

 The necessity for such a division in accordance with th? views of 

 Hall is admitted, but the name is to be rejected, since the rocks. 



•immediately below it are properly not Lower Silurian but tapper 

 C!ambrian, Evidence of a fourth break between the Oriskany 

 and the Corniferous were mentioned, in the erosion of the former 

 in New-York and Ontario, although to the eastward in Graspe, 

 they form a continuous series. The author closed by a tribute 

 to the memory of the venerable Sedgwick, the Nestor of British 

 geologists, who died last Winter, and to the labours of Prof. 

 JHall, who, in his vast work on our palaeozoic geology, has reared 

 '-to himself an imperishable monument. 

 WoL. VII. L No. 3. 



