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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 W. 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 Ver- 

 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- 

 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 Paradoxides. Certain additions having been made to these 

 fossils, Mr. Salter finds that of the whole there are five genera peculiar to the 

 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, Illse- 

 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 

 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- 

 lella, Salter) and by the genera Olenus, Paradoxides, and Dikelocephalus, which 

 most characterize it in Britain as in other regions.* 



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 

 be distinguished by peculiar fossils in any given tract from the prevalent Lower 

 Silurian types, there exists no valid ground for differing from Barrande, de 

 Verneuil, Logan, J ames Hall, and others, by separating this rudimentary fauna 

 from that of the great Silurian series of life of which stratigraphically it con- 

 stitutes the conformable base. And if in Europe but few genera be yet found 

 which are common to this lower zone and the Llandeilo formation (though the 

 Agnostus and Orthis are common to it and all the Silurian strata), we may not 

 unreasonably attribute the circumstance to the fact, that the primordial zone 

 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 prirn- 



* 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. 



