252 ANNUAL OF SCIENTIFIC DISCOVERY. 



underlying primordial shales, as the greatly-developed representa- 

 tives of the Potsdam and Calciferous groups (with part of that of the 

 Chazy), and the true base of the Silurian system." -"The Quebec 

 group, with its underlying shales," this author adds, "is no other 

 than the Taconic system of Emmons ; " which is thus shown to be 

 the natural base of the Silurian rocks in America, as Barrande and 

 De Verneuil have proved it to be on the continent of Europe. 



I take this opportunity 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, and others, by sepa- 

 rating this rudimentary fauna from that of the great Silurian series 

 of life of which stratigraphically it constitutes the conformable base. 

 And if in Europe but few genera be yet found which are common to 

 this lower zone and the overlying formation, we may not unreason- 

 ably attribute the circumstance to the fact that the primordial zone 

 of no 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 primordial zone with 

 the overlying strata into widc-h it graduates ? Let us recollect that 

 a few years only have elapsed since M. de Verneuil was criticized 

 for inserting in his table of the Palaeozoic Fauna of North America a 

 number of species as being common to the Upper and Lower Silu- 

 rian. But now the view of the eminent French academician has 

 been completely sustained by the discovery in the strata of Anticosti, 

 British America, of a group of fossils intermediate in character be- 

 tween those of the Hudson River and Clinton formations, or, in other 

 words, between Lower and Upper Silurian rocks. 



On the continent of Europe an interesting addition has been made 

 to our acquaintance with the fauna of one of the older beds of the 

 Lower Silurian rocks, or the Obolus green-sand of St. Petersburg, 

 by Ehrenberg. He has described and figured four genera and ten 

 species of microscopic Pteropods. It is well to remark that, as the 

 very grains of this Lower Silurian green-sand seem to be in great 

 part made up of these minute organisms, so we recognize, in one 

 of the oldest strata in which animal life has been detected, organisms 

 of the same nature as, and not less abundant than, those which con- 

 stitute the deep sea-bottoms of the existing Mediterranean and other 

 seas. 



Before I quit the consideration of the older palaeozoic rocks, I must 

 remind you that it is through the discovery by Mr. Peach of certain 

 fossils of Lower Silurian a^e in the limestones of Sutherland, Scot- 



^j 



land, combined with the order of the strata, observed in the year 

 1827 by Professor Sedgwick and myself, that the true age of the 

 largest and overlying masses of the crystalline rocks of the High- 

 lauds has been fixed. The fossils of the Sutherland limestone are 

 not indeed strictly those of the Lower Silurian of England and 

 Wales, but are analogous to those of the calciferous sand-rock of 



