Mr. Murchison on the Silurian System of Rocks. 47 



nounce in the order detailed in that table (see Lond. and Edinb. 

 Phil. Mag., vol. iv. p. 370), but I wish to simplify it by the 

 abandonment of double names, as applied to any one formation, 

 and by the adoption of the names of those places only where 

 the respective rocky masses lie in juxtaposition. 



The names finally adopted, and which will be incorporated 

 in a work now in preparation on this subject, are, 



1. Ludlow rocks, divided into upper and lower Ludlow 

 rocks, with a central zone of limestone : in this formation no 

 change of name is proposed. 



2. Wenlock limestone and shale {equivalent, Dudley)* 



3. Caradoc sandstones. This name, supplying the place of 

 the Horderley and May Hill rocks, has been derived from 

 the striking and well-known ridge of Caer Caradoc, on the 

 eastern flanks of which, and lying between it and the Wen- 

 lock Edge, are exhibited those peculiar strata which are the 

 equivalents of the shelly sandstones of Tortworth. 



4. Llandeilo flags (preferred to " Builth and Llandeilo"). 

 When this table is reprinted, there will naturally be found 

 many additions to the organic remains, some identifications 

 of British with foreign species, and numerous corrections. 



Notwithstanding the adoption of these names, there was still 

 required a comprehensive term by which the whole group 

 could be designated, and at once distinguished from the old 

 red sandstone above, and the slaty rocks below. Without 

 such a collective name for the group, I found it impracticable 

 to proceed with the work which I had engaged to complete, 

 it being essential to the clear exposition of the subject, no 

 longer to speak of these deposits as " transition rocks" or 

 " fossiliferous grauwacke." The term ' transition' might in- 

 deed, have been retained, if for no other reason than to im- 

 press upon foreign geologists, (the Germans particularly,) how 

 vast a difference exists between the geological horizon of the 

 mountain or carboniferous limestone and that of the limestones 

 of Ludlow and Wenlock, which are not only separated by 

 many thousand feet of strata from the limestone of the car- 

 boniferous system, but, further, contain an entirely distinct 

 class of organic remains. It was, however, utterly hopeless 

 to use the word 4 transition' in any definite sense as applied 

 to these lower deposits, seeing the extent to which it had 

 been abused. By some it was confined to those older rocks 

 in which the earliest traces of organic remains were sup- 

 posed to be observed, whilst others had more recently so 

 expanded the meaning as to comprehend in it the whole 

 of the carboniferous series ! Thus at a period when, from 

 the rapid advances of the science, it had become indispen- 



