350 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



This sandstone, together with some other subordinate strata, are 

 probably the channel of fossil-communication between the Lower and 

 Upper Silurian stages. 



Oneida Conglomerate. 



This is a group of great importance, from its vast development, 

 especially in length, and from the tokens it bears both of plutonic 

 disturbances, and of certain relations of land and sea at and after the 

 epoch of its deposition. 



It is made up of a continued alternation, but irregular in all 

 respects, of three conformable masses : — 



1st. A conglomerate of variously-coloured, but chiefly white, quartz- 

 pebbles, usually fths of an inch in diameter. 



2ndly. Of white, yellowish, or red quartzose sandstone ; and 



3rdly, and very largely, of red and green shale, highly titaniferous : 

 that is, if the vast formation so named by Sir William Logan be 

 Oneida Conglomerate ; for it is considered to be the Hudson-River- 

 group by Professor H. D. Rogers, according to a conversation with 

 me. Many strong reasons may be brought in favour of either view, 

 in the proper place.* 



Transition. — The upper portions of the Hudson-River-group 

 either having been removed or never laid down in places, we find 

 that the Oneida Conglomerate may rest on Frankfort Slates (H.-R.- 

 group), as in Herkimer County, or on Pulaski shales (H.-R.-group), 

 as in the west part of Oneida County, the distinction or separation 

 being abrupt (Vanuxem) ; or, as we have shown, it may succeed 

 the Grey Sandstone just described. This would appear a natural 

 termination of the Hudson-River-group, and would be an easy and 

 gradual introduction of the Oneida Conglomerate. In regular 

 ascending order, this conglomerate may always be taken as succeed- 

 ing the Hudson-River-group without interpolation and gradually. 



Further east, in the State of New York, along the base of the 

 Helderberg Mountains, where the Clinton, Niagara, and Onondaga- 

 salt groups are very thin, the Oneida Conglomerate is absent, and 

 the Hudson-River-group rises to within a few feet of the Tentaculite-, 



* Professor Rogers merges Oneida Conglomerate into Medina Sandstone, — both 

 together constituting his " Levant Series " in Pennsylvania. 



His brief but clear account of the mineral character of Oneida conglomerate 

 differs little from that given by the New York geologists. It is to the following 

 effect (Johnston's Atlas, 2nd edit., p. 31) : — 



It is a triple formation. The upper member is a white and light-grey, fine- 

 grained, hard sandstone, alternating near its upper limit with beds of red and 

 greenish shale ; the sandstone covered with Fucoids profusely. This is 400 to 500 

 feet thick in Pennsylvania. 



The middle member is a soft, argillaceous, brown sandstone and red shale ; 

 thickest (500 feet) in the mountains which cross the Juniata River. 



The third or lower member is a hard, greenish-grey, massive sandstone (200 

 to 400 feet thick), embracing in its eastern outcrop (as in the Kittatinny and 

 Shawangunk Mountains) thick beds of siliceous conglomerate, made up chiefly 

 of the wreck of previously -formed and disturbed older palaeozoic rocks. 



The upper and middle members constitute the Medina Sandstone of New 

 York. 



