550 Geological Society: Anniversary Address, \%^2. 



In the mean time other obsei'vers had beeiT working otit detailed 

 facts which pointed to the same conchisions. In a part of Cumber- 

 land, Mr. James Marsliall had established tht presence of Silurian 

 deposits, where it was formerly supposed still older rocks prevailed, 

 and more recently Mr. MacLauchlan of the Ordnance Survey, has 

 shown us that all tlie slaty, and in parts metamorphic tracts of North 

 Pembroke, which are coloured in my Silurian map as Cambrian, or 

 in other words, as strata beneath the Llandeilo flags, contain many 

 of the same forms as the Lower Silurian rocks. Before these inquiries 

 had taken place at home, the researches of Professor Sedgwick and 

 myself in Germany and Belgium, and of M. de Verneuil and myself 

 in Russia, had led to the same conclusions, viz. that wherever it 

 exists, the zone of fossiliferous strata cliaracterized by the Lower 

 Silurian Orthidce, are the oldest beds in wliicli organic life has been 

 detected, and that many of the subjacent rocks, sometimes even when 

 in the form of gneiss, mica schist, talc schist, cldorite slate, iSrc. are 

 nothing but metamorphic rocks, in less altered parts of which the 

 same typical fossils are observable. 



If then our researches teacii us that the term Cambrian must 

 cease to be vised in zoological classification, it being in that sense 

 synonymous with " Lower Silurian," we see the true value of having 

 established a type like the latter, which being linked on through in- 

 termediary groups to overlying formations, the age of which was 

 previously well icnown, we have arrived gradatim, and without hypo- 

 thesis, at the apparently true base of the zoological series in Europe. 

 It is right, therefore, tiiat I should announce that the conventional 

 line which was set up in the map of the Silurian region, between the 

 Lower Silurian and the Cambrian rocks, and which has been adopted 

 by Mr. Greenough, has no longer any reference to strata identified 

 by distinguishing organic remains, for the same fossils are found in 

 strata on each side of that demarcation. Such lines of division, 

 however, when viewed as the signs of local phaenomena, are not- 

 withstanding highly useful, both as indicating changes of litholo- 

 gical character, great lines of disruption and lower divisions of the 

 same palaeozoic group. In short, all researches up to this day have 

 led to the belief, that the Lower Silurian fossils were the earliest 

 created forms, and that this " protozoic" type prevailed during that 

 vast succession of time which was occupied in the acciunulation of 

 all the older slaty rocks, until the Upper Silurian period, when new 

 creatures were called into existence, and when the earlier forms 

 diminished and were succeeded by a profusion of chambered shells 

 which so abundantly characterize that epoch. 



This, Gentlemen, is I trust a good step gained. To establisii upon 

 sound data the true theorj^ of organic succession in tiie oldest fonns 

 of life, is surely important, and we ought to rejoice that the Bri- 

 tish islands have afforded us tlie means systematically to work out 

 the question. Ascending then from these lowest types, the Upper 

 Silurian zone is one of great distinctness in England, and in the 

 Baltic — in the northern provinces of Russia and in North Ame- 

 rica ; the Wenlock, Dudley and Ludlow fossils having been abun- 



