10 The Rensselaer Grit Plateau. 



occurs in the order named."* These grits and conglomerates are now- 

 regarded by Mr. Dale as the equivalents of the Oneida conglomerates 

 of Upper Silurian age. 



The descriptions just quoted correspond so closely with those given 

 by Sir Wm. Logan for the sandstone and slates of the Sillery formation 

 as developed in Quebec and on the north-west coast of Newfoundland, 

 that but little doubt can exist as to their being portions of the same 

 geological series. The arrangement of strata at Rensselaer is evidently 

 complicated by faults, folds and overturns as in Quebec which have 

 been so extensive as in places to bring horizons, otherwise widely 

 separated, contiguous to each other and in some cases even to have 

 placed the newer formation beneath the older. Thus at Orleans 

 Island, below Quebec, the strata which hold the Black-River-Trenton 

 fauna, arc now beneath those holding the Sillery-Levis fauna, the whole 

 series being apparently conformable. So also at several places along the 

 coast below Meiis the Trenton beds are enfolded and appear to consti- 

 tute an integral part of the Sillery red and green slates. From the 

 description of the rocks of the Rensselaer area a precisely similar 

 arrangement would appear to exist and the Sillery red and green slates, 

 grits and fine conglomerates appear to form a higher portion of the series 

 above the " Hudson River " or Trenton formation. The relations of 

 the several series in the two districts of Quebec and New York appear 

 to be very similar. 



It is therefore natural to suppose that the view taken by Sir Wrrv 

 Logan, after a careful study of the strata in both countries, that these 

 represent portions of the same great series, is a correct one ; and so 

 strongly was he impressed with this fact that in the great geological 

 map of Canada and the northern United States, (1866,) he so mapped 

 them as portions of the Sillery and Levis formations, h is interesting to 

 noteherealsothatinQuebecthe conclusions firstreached as t^> thestratigra- 

 phical sequence of this series coincided almost exactly with those put forth 

 by Mr. Dale in his recent report, in which the Sillery and Levis rocks 

 were regarded as straligraphically newer than the Hudson River 



The Rensselaer Grit Plateau in New York, by T. Nelson Dale, 13th Ann. Rep, 

 L'.S Geol. Survey, pp. jo6, 307. 



