432 
THE GEOLOGIST. 
In an able review of this subject, Mr. Sterry Hunt thus expresses himself: 
*' We regard the whole Quebec group, with its underlying primordial shales, 
as the greatly developed representatives of the Potsdam and Calciferous groups 
(into part of that of Chazy), and the true base of the Silurian system." " The 
Quebec group, with its underlying shales," this author adds (and he expresses 
the opinion of Sir "VV. Logan), "is no other than the Taconic system of Em- 
mons which is thus, by these authors, as well as Mr. James Hall, shown to 
be the natural base of the Silurian rocks in America, as Barrande and De Ver4 
neuil have proved it to be on the continent of Europe. 
In our own country a valuable enlargement of our acquaintance with the 
relations of the primordial zone to the overlying members of the Silurian rocks, 
has been made through the personal examination of Mr. Salter, aided by the 
independent discoveries of organic remains by MM. Homfray and Ashe, of 
Tremadoc. 
It has thus been ascertained, that the lower member only of the deposit^ 
which has been hitherto merged under the name of Lingula-flags, can be con-i 
sidered the equivalent of the primordial zone of Bohemia. In North Wales} 
that zone has hitherto been mainly characterized by Lingula and the crusta- 
ceans Olenus and Paradosides. Certain additions having been made to these 
fossils, Mr, Salter finds that of the whole there are five genera peculiar to thej 
lower zone, and seven which pass upwards from it into the next overlying band! 
or the Tremadoc slate. But the overlying Tremadoc slate, hitherto also 
grouped with the Lingula-flags, is, through its numerous fossils (many of them 
of recent discovery), demonstrated to constitute a true lower member of the ; 
Llandeilo formation. Eor, among the trilobites, the well-known Llandeilo forms.; 
of Asaphus and Ogygia range upwards from the very base of these slates. Again,, 
seven or eight other genera of trilobites, which appear here for the first time, 
are associated with genera of mollusks, and encrinites, which have lived through'; 
the whole Silurian series. Such, for example, are the genera Calymene, Illae-., 
nus, among crustaceans; the Lingula, Orthis, Bellerophon, and Conularia,..! 
among mollusks, together with encrinites, corals, and that telling Silurian] 
zoophyte, the Graptolite. By this proof of the community of fossil types, aS'j 
well as by a clear lithological passage of the beds, these Tremadoc slates are.) 
thus shown to be indissolubly connected with the Llandeilo and other Silurian 
formations above them ; whilst, although they also pass down conformably into.,: 
the zone primordiale, the latter is characterized by the linguloid shells (Lingu-'j 
lella, Salter) and by the genera Olenus, Paradoxides, and Dikelocephalus, which ; 
most characterize it in Britain as in other regions.* i 
I take this opportunity, however, of reiterating the opinion I have expressed ^ 
in my work, " Siluria," that to whatever extent the primordial zone of Barrande j 
be distinguished by peculiar fossils in any given tract from the prevalent Lower .i 
Silurian types, there exists no valid ground for differing from Barrande, det 
Verne nil, Logan, James Hall, and others, by separating this rudimentary fauna ' 
from that of the great Silurian series of life of which stratigraphically it con- j 
stitutes the conformable base. And if in Europe but few genera be yet found i 
which are common to this lower zone and the Llandeilo formation (though the i 
Agnostus and Orthis are common to it and all the Silurian strata), we may not -i 
unreasonably attribute the circumstance to the fact, that the primordial zone i 
of no one country contains more than a very limited number of distinct forms. ; 
May we not, therefore, infer that in the sequel other fossil links, similar to ; 
those which are now known to connect the Lower and Upper Silurian series — 
which I myself at one time supposed to be sharply separated by their organic . 
remains — will be brought to light, and will then zoologically connect the prim- , 
* In the last edition of Siluria the distinction was drawn between the lower and 
upper Lingula-flags, but the fauna of the latter is now much enlarged. 
