GEOGNOSY OF THE APPALACHIANS. 483 
From the part which the ruins of these rocks play in the produc- 
tion of succeeding sediments it is not always easy to define the limits 
between the ancient mica-schists and the Cambrian strata in these 
northeastern regions. It is not impossible that the two may grad- 
uate into each other, as some have supposed, in Newfoundland and 
Nova Scotia, but until farther light is thrown upon the subject I 
am disposed to regard the relation between the two as one of der- 
ivation rather than of passage. 
We have already alluded to the history of the rocks of the 
White Mountains, formerly looked upon as primary, and by Jack- 
son described as an old granitic and gneissic axis uplifting the more 
recent Green Mountain rocks. Their manifest differences from the 
more ancient gneiss of the Adirondacks, and their apparent super- 
to 
in 1846 to look upon the White Mauntains as altered strata be- 
longing to the Levant division of their classification, correspond- 
g to the Oneida, Medina and Clinton of the New York system. 
In 1848 Sir William Logan came to a somewhat similar conclusion. 
Accepting, as we have seen, the view of Emmons that the strata 
about Quebec included a portion of the Levant division, and re- 
garding the Green Mountain gneisses as the equivalents of these, 
he was induced to place the White Mountain rocks still higher in 
the geological series than the Messrs. Rogers had done, and ex- 
pressed his belief that they might be the altered representatives 
of the New York system from the base of the Lower Helderberg 
to the top of the Chemung ; in other words, that they were not 
Middle Silurian, but Upper Silurian and Devonian. This 
adopted and enforced by me,* was farther supported by eaii ii in 
1860, and has been generally accepted up to this time. In 1870, 
however, I ventured to question it, and in a published letter ad- 
dressed to Professor Dana, concluded from a great number of 
facts that there exists a system of crystalline schists distinct from, 
and newer than, the Laurentian and Huronian, to which I gave the 
provisional name of Terranovan, constituting the third or White 
Mountain series, which appears not only throughout the Appalach- 
ians, but westward to the north of Lake Ontario, and around and 
beyond Lake Superior.¢ Although I have in common with most 
"Geol. Survey o f Canada, Report 1847-48, p. 58; also Amer. Jour. Sci., II, ix, 19. 
t Amer. Jour. Sci., II, 1, 83. 
AMER. NATURALIST, VOL. V. 31 
