452 Geological Society : — Anniversary of 1839 . 



island has of course been obtained bj"^ a careful attention to the po- 

 sition and supei-position of the mineral masses, and by tracing the 

 geographical continuity of the strata, almost mile by mile, from Cape 

 Wrath to the Land's End. In this manner he has connected the 

 rocks of Scotland with those of Cumberland ; these again with those 

 of Wales ; and the Welsh series, though more obscurely, with that 

 of Devonshire and Cornwall. In this survey he has constantly kept 

 before his eyes a distinction, known indeed before, but never before 

 so carefully and systematically employed, between the slaty cleavage 

 of rocks and their stratification ; for the directions of these two 

 planes, though each wonderfully persistent over large ti'acts, never, 

 except by accident, coincide. He has taken for his main guide the 

 direction of the strata, or, as it is called, the strike of the beds ; and 

 in such a course, the theory of Elie de Beaumont respecting the 

 parallelism of contemporaneous elevations, whether true or false, 

 could not fail to give an additional interest to geological researches, 

 conducted on so large a scale as those of Prof. Sedgwick. Mr. 

 INIurchison's mode of investigation may be described thus : that he 

 has applied, for the first time, to the rocks below the Old Red Sand- 

 stone, the method of classification previously employed with so much 

 success for the Oolites. It is truly remarkable, that Nature has 

 placed in this our corner of the world, series, probably the most 

 complete which exist, of both these groups of strata ; and as the 

 Oolites of England have long been the type of that portion of Euro- 

 pean geology, the Silurians of Wales may perhaps soon be recog- 

 nized as the standard members of a still more extensive range of 

 deposits. As if Nature wished to imitate our geological maps, she 

 has placed in the corner of Europe our island, containing an Index 

 Series of European formations in full detail. 



The Carboniferous, Old Red, Silurian and Cambrian systems have, 

 by many writers, up to the present time, been all comprehended in 

 the term "transition rocks", so far as that term has been used with 

 any definite application at all. The analysis of this vague group 

 into these distinct portions removes the confusion and perplexity 

 which have hitherto prevailed in this province of geology. Prof. 

 Sedgwick has further proposed to apply the term PalcBozoic, and 

 Mr. Murchison that of Protozoic, to the rocks which constitute the 

 Cambrian and Silurian systems. 



How far these appellations are useful, we shall see when we have 

 had speculations presented to us in Avhich they are familiarly used ; 

 for necessity is the best apology, and convenience the best rule, of 

 innovations in scientific language. In the names applied to the 

 members of the Silurian system, Mr. Murchison, following those 

 examples of geological nomenclature which have been most cleai-ly 

 understood and most generally adopted, has borrowed his terms from 

 localities in which standard types of each stratum occur. If the 

 Silurian system be as exclusively diffused as some indications seem 

 to imply, we may find the Ludlow Rocks in Scandinavia, and 

 the Caradoc Sandstone even in Patagonia. Whether a like identi- 

 fication of the more ancient rocks of the Cambrian series with the 



