TACONIC QUESTION IN GEOLOGY. 259 
able superposition of the upper members of the Champlain division upon the lower ones ; 
a break occuring at the summit of the Trenton. 
It is impossible not to connect these conditions in the Ottawa and Hudson valleys 
with those already noticed in eastern Pennsylvania, and in Orange county, New York, 
where the Oneida sandstone, which, as we have seen, is continuous with the upper part of 
the Loraine shales, is found to rest unconformably upon the strata of the First Graywacke. 
$111. Considerable moyements are thus seen to have marked both the beginning and 
the close of the Chazy-Trenton period, and it is evident that the absence, in any district, of 
the characteristic limestone of this time, between the First and Second Graywackes, might 
result either from non-deposition or from erosion. Evidence of the latter is afforded in the 
area just described in the Ottawa basin; while, at the same time, there is not wanting 
evidence that this limestone-mass, so well marked by its thickness, and the persistence of 
its lithological character over great areas in eastern North America, elsewhere thins out, 
and either disappears entirely, or loses its ordinary lithological characters. Thus, while in 
Canada, at points as widely separated as Beauport, Montreal, Ottawa, Lake Simcoe and the 
shores of Lake Huron, it appears with a thickness of from 600 to 750 feet (being every where 
followed by the Utica and Loraine. shales), it is in Lewis county, New York, diminished to 
300 feet, at Trenton Falls to 100 feet, and, it is said, to thirty feet in the Mohawk Valley; 
thinning-out and disappearing to the southeast, according to Conrad ; but, as will subse- 
quently appear, probably represented along this eastern border, by argillaceous beds, which, 
but for their organic remains, would not be recognized as of Trenton age. 
§112. The bearing of the paleontological investigations made by the geological survey 
of Canada on the question of the age of the eastern Graywacke, or so-called Hudson-River 
group of rocks, was discussed by James Hall, in a note to his Geology of Wisconsin, in 1862 
(page 443). He there alluded to the evidence furnished by organic remains found in the 
Hudson River-slates in Vermont and Canada, “ which prove conclusively that these slates 
are to a great extent of older date than the Trenton limestone,” though probably newer 
than the Potsdam. He moreover remarked that “the occurrence of well-known forms of 
the second fauna . . . . in intimate relation with, and in beds apparently constituting 
a part of the series, along the Hudson River, requires some explanation. Looking critically 
‘at the localities in the Hudson valley which yield the fossils, we find them of limited and 
of almost insignificant extent. Some of them are on the summits of elevations, which are 
synclinal axes . . . . where the remains of newer formations would naturally occur. 
Others are apparently unconformable to the rocks below, or are entangled in the folds of 
the strata, . . . . whilethe enormous thickness of beds exposed is almost destitute 
of fossils.” In view of all these facts, Hall, while still retaining the name of Hudson-River 
group as the designation of the fossiliferous strata which elsewhere are found to occupy 
a horizon between the Utica slate and the Oneida sandstone (otherwise called Pulaski and 
Loraine shales), concludes that the name of Hudson-River group cannot properly be extended 
to the great mass of strata which have hitherto borne that name; and which, according to 
him, “are separated from the Hudson-River group proper by a fault not yet fully ascer- 
tained.” 
§ 113. It should, however, be remembered that although the Hudson-River group was, 
through the paleontological publications of the New York survey, identified with the 
. Loraine shales only; the name, as at first given by Vanuxem, was made to include two 
