ANNIVERSARY ADDRESS OF THE PRESIDENT. XXXV11 



mony to his correct rendering of facts which, in my opinion (and I 

 know the ground well), only require to be seen to be believed. 



The oldest-known rock in Britain is the Laurentian gneiss in the 

 north-west of Scotland *. On this, certain strata lie which have been 

 termed Cambrian. They are quite unmetamorphosed, and rest in 

 the highest degree unconformably on the denuded convolutions of 

 the intensely metamorphosed gneiss. The interval of time, there- 

 fore, that elapsed between the conclusion of the formation of the gneiss 

 and the beginning of the deposition of the overlying conglomerate 

 was geologically of the longest; for I believe that, in this as in 

 other cases, 1st, the metamorphic structure was developed deep 

 beneath the surface, and, 2nd, these rocks were upheaved, contorted, 

 and greatly denuded before the newer strata were formed above them. 

 Therefore, except that they occur together, there is no immediate 

 connexion between the underlying and overlying formations ; and the 

 vastness of the intervening denudation proves that the interval repre- 

 sented by the unconformity must have been of extreme length. 



The extremely metamorphic state of the Scottish Laurentian rocks 

 makes it highly improbable that fossils should be found in them. 

 But in a thick band of limestone in their supposed equivalents in 

 Canada, Sir William Logan considers that he has found the remains 

 of Corals, — an opinion in which I agree. If this be so, the " Primor- 

 dial Zone," in a literal sense, vanishes ; and the supposed absence 

 of fossils in the Cambrian rocks of Scotland f may have no higher 

 value in palaeontology than the absence of organic remains in the 

 Bunter sandstone of England. 



It is also not quite certain, though it is probable, that the Cam- 

 brian rocks of Scotland are the equivalents of those of England and 

 Wales, for this reason, that while in Wales there is perfect con- 

 formity and a gradual passage from the Cambrian rocks into the 

 Lingula-flags, in Scotland the Lingula-flags are absent, and the 

 equivalents of the Llandeilo beds lie quite unconformably on the 

 Cambrian strata. Sir Roderick Murchison has drawn special atten- 

 tion to this unrepresented interval J; and, as I shall bye-and-bye show 

 that in Caernarvonshire the Llandeilo beds are probably unconform- 

 able to the Lingula-series, it is not surprising that in Sutherland 

 Llandeilo beds should lie unconformably on what are believed to be 

 Cambrian strata. If so, this unconformity is closely connected, as I 

 shall show, with the great break in the succession of species between 

 the so-called Primordal Zone and the Llandeilo flags. 



Lingula-flags. — The Lingula-flags of Wales § contain a small but 

 well-marked assemblage of fossils, consisting, as at present known, of 

 about 6 genera and 20 species of Trilobites ||, 1 Hymenocaris, 3 Bra- 

 chiopods (2 Lingular and an Orthis), and 1 Bryozoon (Dictyonema)%. 



* See Memoirs and Map by Sir Roderick Murchison and Mr. Geikie. 

 t As yet, they have scarcely been searched. \ Siluria, 2nd ed., p. 197. 



§ From 5000 to 6000 ft., where thickest. 



|| Dikelocephalus, Agnostus, Olenus (7), Conocephalus, Ellipsocephalus, and 

 JParadoxides. 

 ^[ I omit the Annelides, as they do not affect my argument. 



