gS; REPORT — 1861. 



nic group of Emmons * with his own primordial Silurian fauna of Bohemia and 

 other parts of Eui'ope ; and although that soimd palajontologist, Mr. James Hall, 

 has not hitherto quite coincided with M. Barrande in some details f, it is evident 

 tliat the primordial fauna occurs in many parts of North America. And as the true 

 order of succession has been ascertained, we now know that the Taconic group is 

 of the same age as the lower Wisconsin beds described by Dale Owen, with their 

 ParadoxideSf Dikelocephalus, &c., as well as of the lower portion of the Quebec rocks, 

 with their Cmiocephalm, Axionellm, &c., described by Logan and Bmings. Of the 

 ciystalline schists of Massachusetts, containing the noble specimen of Paradoxides 

 described by W. Eogers, and of the Vermont beds, with their OUni, it follows that 

 the Primordial Silurian Zone of Barrande (the lower Lingula-flags of Britain) is 

 largely represented in North America, however it may occupy an inverted position 

 ill some cases, and in others be altered into ciystalline rocks. 



In determining this question due regard has been had to the great convulsions, 

 inversions, and breaks to which these ancient rocks of North Ajoierica have been 

 subjected, as described by Professors Heniy and W. Rogers. 



In an ablo review of this subject, Mr. Stei-ry Hunt thus expresses himself: — 

 '■^ We regard the whole Quebec group, with its imderlyiug primordial shales, as the 

 gl-eatly developed representatives of the Potsdam and Calcilerous gi-oups (with part 



of that of Chazy), and the true base of the SUui-ian system The Quebec gi'oup, 



with its imderlying shales," this author adds (and he expresses the opinion of Sir 

 W. Logan), " is no other than the Taconic system of Emmons ;" whicn is thus, by 

 these authors, as well as Mr. James Hall, shown to be the natm'al base of the Silu- 

 rian rocks in America, aa Barrande and De Vemeuil have proved it to be on the con- 

 tinent of Europe. 



In GUI' own coimtiy a valuable enlargement of oui' acquaintance with the relations 

 of the piTmordial zone to the overling 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. Ilom&ay and Ashe, of Tremadoc. 



It has thus been ascertained that the lower member only of the deposit, which has 

 been hitherto merged imder the name of Lingida-llags, can be considered tho equi- 

 valent of the primordial zone of Bohemia. In North Wales that zone lias hitherto 

 been mainly characterized by Lingida and the crustaceous 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 up- 

 wards from it into the next overlying band or the Tremadoc slate. But the over- 

 lying Tremadoc slate, hitherto also gi-ouped -svith 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. For, among the trilobites, the well- 

 known Llaudeilo forms of Asaphtts and 0(/ygia range upwards from the veiy 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 encnnites 

 which have lived through the whole Sihu'ian series. Such, for example, are the 

 genera Calymene, lUcenus, among crustaceans; the Lingula, Orthis, Belkrojihon, 

 and Comdaria among mollusks, together with encrinites, corals, and that telling 

 Silurian zoophyte, the Graptolite. By this proof of the community of fossil tj^es, 

 as well as by a clear lithological passage of the beds, these Tremadoc slates are thus 

 shown to be iudissolubly connected with the Llandeilo and other Silurian forma- 

 tions above them ; whilst, although tliey also pass down confonnably into the zone 

 primordiale, tho latter is characterized by the lingidoid shells (Ltuf/tdella, Salter) 

 and by tho genera Olemis, Paradoxides, and Dikelocephalus, which most charac- 

 terize it in Britain as in other regions J, 



extensive conglomerates and marls of triassie age, and these by deposits charged with fos- 

 sils of the Lias. 



* Tlie Sihu'ian classification was proposed by me in 1835, and in the following year (183G) 

 Dr. Emmons suggested that his black shale rocks, which he called Taconic, were older than 

 any I described. 



t Nor arc the writings of the Professors W. B. and S. D. Eogers in unison with tho 

 opinions of the authors here cited. 



X In the last edition of ' Sihu-ia ' the distinction was drawn between the lower and upper 

 Liugida-flags, but the faima of the latter is now much enlarged. 



