246 The Taconic Question Restated. [March 
ferences between Billings and Logan on these points appear in 
the volume of the former on “ Paleozoic Fossils,’’* and more 
fully in the instructive correspondence of Billings with Jewett 
and Marcou, lately published by the latter in his paper on the 
Taconic system in 1885.7 
§.24. James Hall, who had in 1857 declared that the graptolitic 
slates found in conjunction with the Sparry Lime-rock at Pointe 
Levis, the Levis limestone of Logan, were at the summit of the 
Hudson River group,—employing this term, as he had always 
done, as synonymous with Loraine shales,—was led by the palæ- 
ontological discoveries in Vermont, and near the city of Quebec, 
to reconsider the age of this so-called group and the true signifi- 
cance of the term. In his “ Report on the Geology of Wiscon- 
sin” in 1862 (p. 443), he referred to the evidence furnished by | 
organic remains in the rocks of the Graywacke belt in the prov- 
ince of Quebec and in Vermont, “ which prove conclusively that 
these slates are to great extent of older date than the Trenton 
limestone,” though probably newer than the Potsdam. He re- 
marked, moreover, 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 these fossils, we find 
them of limited and almost insignificant extent. Some of them 
are on the summits of elevations which are synclinal axes, .. . 
“where the remains of new formations would naturally occur. 
Others are apparently unconformable to the rocks below, or are 
entangled in the folds of the strata, .. . while the enormous 
thickness of beds exposed is almost destitute of fossils.’ He 
hence concluded that the name of Hudson River group cannot 
properly be extended to the great mass of strata which had 
hitherto borne that name, but which he now regarded as distinct 
from “the Hudson River group proper.” 
§ 25. Thus while still retaining for the Loraine shales the name 
under which Vanuxem had, in 1842, included alike these shales 
and the great underlying mass of older strata belonging to two 
lower horizons which constitute by far the larger portion of the 
* Geological Survey of Canada, 1865; Paleozoic Fossils, vol. i. passim. 
2 Proc. Amer. Acad. Sciences, New Series, vol. xii. pp. E See also therein 
the letters of Emmons and and Marcou, pp. 1 184-201. 
