Geological Society of London. 173 



special case^ how far tliis will be so. Yet the great works of Messrs 

 Murchison and Sedgwick, tending to the establishment of a classification 

 of the strata below the old red sandstone (works which, on all accounts 

 we must consider as a joint undertaking), apjpear already to offer an 

 augiiry which can hardly be doubtful, of this influence and permanence. 

 Mr Murchisou's appellation of the " Silurian System" has alread}' been 

 adopted by MM. Elie de Beaumont and Dufresnoy, who have given it 

 currency on the Continent : M. Bone and M. de Verneuil announce the 

 diffusion of " Silurian" rocks in Servia and the adjacent parts of Turkey 

 in Europe ; our own members, Mr Hamilton aid Mr Strickland, have 

 extended their range to the Thracian Bosphorus ; M. Forchhammer of 

 Copenhagen, visited the "Silurian region" to recognise the rocks of 

 Scandinavia ; and MM. Omalius D'Halloy and Duraont have just ex- 

 plored it, to establish a parallel between its deposits and those of Bel- 

 gium. It will be observed that some of the districts thus mentioned are 

 out of the limits of our geological Home circuit ; and if the identification 

 be really and permanently established in these cases, will extend the li- 

 mits within which the parallelism of geological series can be asserted : 

 and this is, in effect, what we have a right to look for, sooner or later, in 

 the progress of geological science. As we must be careful not to apply 

 our domestic types without modification to other regions, so must we 

 take care not to despair of modifying our scheme, so that it shall be far 

 more extensively applicable than it at first appeared to be. Of this pro- 

 gress of things, examples are too obvious and too recent to require to be 

 pointed out. 



The labours of Professor Sedgwick refer to the " Cambrian System," 

 which lies beneath the Silurian system, occupying much of North Wales, 

 Cumberland, and a great part of Scotland ; while the Silurian sj-stem 

 spreads over a great part of South Wales and the adjoining English couu- 

 ties. The classification of the rocks of this portion of our island to which 

 Professor Sedgwick has been led, though laid before jou only at a recent 

 meeting, is the fruit of the vigorous and obstinate struggles of many 

 years, to mould into system a portion of geology which appeared almost 

 too refractory for the philosopher's hands ; and which Professor Sedg- 

 wick grappled with the more resolutely, in proportion as others shrank 

 away from the task perplexed and wearied. I need not attempt any de- 

 tailed view of his system : his First Class of Primary Stratified Rocks oc- 

 cupies the Highlands of Scotland and the Hebrides, and appears in Ang- 

 lesea and Caernarvonshire ; the crystalline slates of Skiddaw Forest, and 

 the Upper Skiddaw slate-series come next. Above these is his Second 

 Class, or Cambrian and Silurian System. The Cambrian is divided into 

 Lower and Upper Cambrian, of which the former includes all the Welsh 

 series under the Bala limestone ; the two great groups of green roofing 

 slate and porphyry on the north and south sides of the mineral axis of the 

 Cambrian Moiuitains (of which groups the position had previously been 

 uiisunderstood), and parts of Cornwall anil South Devon. The Upper 



