1887] _ The Taconic Question Restated. 245 
Calciferous divisions of the New York system. The Red Sand- 
rock included in this belt in Vermont was, however, subsequently, 
from its fauna, referred by Billings of the Canada geological 
survey to a lower horizon, the so-called Lower Potsdam, and an 
attempt was made to establish a Potsdam group beneath the 
Quebec group, including both the Red Sand-rock (which Logan, 
in 1859, had placed above the summit of the Hudson River 
group) and a group of strata at Farnham in Quebec, which are, 
however, of Chazy if not of Trenton age. ; 
§ 23. The subsequent history of Logan’s endeavor to separate 
the Graywacke series, as displayed near the city of Quebec, into 
what he called the Levis, Lauzon, and Sillery divisions of the Que- 
bec group, and his conjecture that the apparent order of super- 
position in the section there exposed represents the real or true 
order has been elsewhere told in detail. By his adoption of 
this conjecture the Levis or Sparry Lime-rock was put at the 
base, and the massive green Sillery sandstone at the summit of 
a Graywacke series of many thousand feet, all of which was but 
a reaffirmation of the old hypothesis of 1855, which had made 
this sandstone the Oneida, and the underlying gray sandstones, 
with shales and limestones, the equivalent of the Loraine. That 
this apparent order was contrary to palzontological evidence was 
pointed out by Billings, who insisted that the horizon of the 
Sparry Lime-rock, and its adjacent Phyllograptus shales, was 
somewhat above the typical Calciferous Sand-rock of New York, 
and that the massive green sandstones belonged to a much lower 
horizon, 
Logan, although he had borrowed from Emmons the concep- 
tion that the great Graywacke series was really below the horizon 
of the Trenton limestone, still adhered to the stratigraphical 
scheme which he had framed when he believed that the section 
at Quebec and Pointe Levis represented the Loraine shale, with 
a great overlying mass of green sandstones with conglomerates 
and red shales, corresponding to the Oneida of the New York 
system. These sandstones, he now thought, might correspond 
to the St. Peter’s sandstone of the Upper Mississippi, and to the 
sandstones and shales which in parts of the Ottawa basin appear 
in the Chazy subdivision. The history of all this has been set 
forth in the writer’s volume on “ Azoic Rocks, etc.”? The dif- 
* Second Geological Survey of Pennsylvania, Report E, 1878. 
