48 Mr. Murchison on the Silurian System of Rocks. 



sable to define the boundaries of groups naturally distinct 

 from each other, dissimilar things were still confounded un- 

 der one common name ! and hence every geologist with 

 whom I am acquainted had been for some time agreed upon 

 the expediency of obliterating the term. The name * trans- 

 ition* is, in truth, not applicable to any one class of stra- 

 tified deposits in preference to another. Thus, for example, 

 within the area of a map now preparing for publication and 

 embracing parts of ten counties only, I shall be able to show 

 transitions into every formation, beginning with the inferior 

 oolite and terminating in descending order with the Llan- 

 deilo flags, many thousand feet below the old red sandstone ; 

 whilst the latter overlie other fossiliferous masses, the rela- 

 tive ages of which yet remain to be worked out ! In va- 

 rious memoirs read before the Geological Society I have de- 

 scribed these rocks as " fossiliferous grauwacke," but this 

 term is in reality a misnomer, as the group contains -few if 

 any strata of the true grauwacke of German mineralogists. 

 But whilst this system contains no such beds, it is underlaid 

 and sometimes in discordant stratification, by a vast series of 

 slaty rocks, in which much genuine grauwacke is exhibited. 

 It was therefore manifest that if used at all in geological no- 

 menclature, the term * grauwacke' must be rejected as inappli- 

 cable to the first great system below the old red sandstone, 

 and restricted to rocks which were ?ww proved to be of much 

 higher antiquity. My friend Professor Sedgwick will doubtless 

 soon dispel the obscurity which hangs over these grauwacke 

 rocks, with which his labours in Wales and Cumberland have 

 so well enabled him successfully to grapple. 



To return, however, to the system under review, I was 

 urged by leading geologists both at home and abroad to pro- 

 pound an entirely new name for it. In consonance, therefore, 

 with those views which have rendered the names used by En- 

 glish geologists so current throughout the world, I venture to 

 suggest, that as the great mass of rocks in question, trending 

 from south-west to north-east, traverses the kingdom of our 

 ancestors the Silures, the term " Silurian system" should be 

 adopted as expressive of the deposits which lie between the 

 old red sandstone and the slaty rocks of Wales, including, as 

 above detailed, the Ludlow, Wenlock, Caradoc, and Llandeilo 

 formations. One of the largest of these formations, to which, 

 indeed, the Llandeilo flags are frequently subordinate, has 

 been named after the bold and picturesque ridge of Caer 

 Caradoc in Shropshire. 



I further propose that the system be subdivided into 

 " Upper" and " Lower Silurian rocks," the former em- 



