BRITISH ASSOCIATION MEETING. 



433 



ordial zone with the overlying strata into which it graduates ? Let us recol- 

 lect, that a few years only have elapsed since M. de Verneuil was criticised 

 for inserting, in his table of the Palaeozoic Eauna of North America, a number 

 of species as being common to the Lower and Upper Silurian. But now the 

 view of the eminent French Academician has been completely sustained by the 

 discovery in the strata of Anticosti, as worked out by Mr. Billings under the 

 direction of Sir W. Logan, 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. In like manner, a similar inter- 

 lacing seems already to have been found, in North America, between the 

 Quebec group, with its primordial fossils, and the Trenton deposits, which are, 

 as is well known, of the Llandeilo age. 



I have thus spoken out upon the fitness of adhering to the classifications de- 

 cided upon by Sir Henry de la Beche and his associates long before I had any 

 relation to the Geological Survey, and which places the whole of the Lingula 

 flags of Wales as the natural base of the Silurian rocks. For English geolo- 

 gists should remember that this arrangement is not merely the issue of the 

 view I have long maintained, but is also the matured opinion of those geolo- 

 gists in foreign countries and in our colonies, who have not only zealously 

 elaborated the necessary details, but who have also had the opportunities of 

 making the widest comparisons. 



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 our eminent associate, 

 Ehrenberg. He has described and figured f four genera and ten species of 

 microscopic Pteropods, one of which he names Panderella Silurica; the 

 generic name being in honour of the distinguished Russian palaeontologist, 

 Pander, who collected them. 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 recognise, in one of the oldest strata in which animal 

 life has been detected, organisms of the same nature, and not less abundant, 

 than those which constitute 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. C. Peach, of certain fossils of 

 Lo\ver Silurian age in the limestones of Sutherland, 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 Highlands 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 North America. The 

 Maclurea is indeed known in the Silurian limestone of the south of Scotland ; 

 but the Ophileta and other forms are not found until we reach the horizon of 

 North America. Now, these fossils refer the zone of the Highland limestone 

 and associated quartz-rocks to that portion of the Lower Silurian which forms 

 the natural base of the Trenton series of North America, or the lower part of 

 the Llandeilo formation of Britain. The intermediate formation — the Lingula 

 " flags" or £f zone primordiale" of Bohemia — having no representative in the 

 North- Western Highlands, there is necessarily a complete unconformity between 

 the fossil-bearing crystalline limestones and quartz-rocks with the Maclurea, 

 Murchisonia, Ophileta, Orthis, Orthoceratites, &c, and those Cambrian rocks 

 on which they rest. 



A great revolution in the ideas of many an old geologist, including myself, 



* See Russia and the Ural Mountains, 

 t Monats-Bericht d. Konig. Akad. der Wiss. Berlin, 18 April, 1861. 

 VOL. IV. 3 A 



