406 Sir Roderick 1. Murchison^s 



tersburg,* by our eminent associate Ehrenberg. He has descr?-" 

 bed and figured f four genera and ten species of microscopic Pte- 

 ropods, one of which he names Panderella Silurica, the generic 

 name being in honour of the distinguished Russian palaeontolo- 

 gist Pander, who collected them. It is well to remark, that as 

 the very grains of the Lower Silurian green sand seem to be in 

 great part to be made up of these minute organisms, so we re- 

 cognize, 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 constitute the deep sea bottoms of the existing 

 Mediterranean and other seas. 



" Before I quit the consideration of the older paloeozoic rocks I 

 must remind you that it is through the discovery, by Mr. C. Peach 

 of certain fossils of Lower Silurian asre in the limestones of Suth- 

 erland, combined with the order of the strata observed in the 

 year 182*7 by Professor Sedgwick and myself, that the true age of 

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

 lands have 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 as- 

 sociated 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 inter- 

 mediate formation — the ' Lingula flags' or zone j^^^i^^ordiale of 

 Bohemia — having no representative in the North-western High- 

 lands, 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, in- 

 cluding myself, has thus been eff'ected. Strengthened and con- 

 firmed as my view has been by the concordant testimony of 

 Ramsay, Harkness, Geikie, James and others, I have had no hesi- 

 tation in considering a very large portion of the crystalline strata of 



* See " Russia and the Ural Mountains." 



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



