Silurian System of Rocks. — Murchison. 81 
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 Wenlock 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 be found many additions to the 
organic remains, some identifications of British with foreign, 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 "fossilif- 
erous grauwacke." The term "transition" might indeed, have been 
retained, if for no other reason than to impress 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 Dudley and Wenlock, which are not only separated 
by many thousand feet of strata from the limestone of the carbonifer- 
ous system, but further, contain an entirely distinct class of organic 
remains. It was, however, utterly hopeless to use the word "transi- 
tion" 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 
supposed to be observed, whilst othei's 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 indispensable to define the boundaries of groups naturally 
distinct from each other, dissimilar things were still confounded under 
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 "transition" is in truth, not applica- 
ble to any one class of stratified deposits in preference to another. 
Thus, for example, within the area of a map now preparing for publi- 
cation 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 Llandeilo flags, 
many thousand feet below the old red sandstone ; whilst the latter 
overlie other fossiliferous masses, the relative ages of which yet remain 
to be worked out ! In various memoirs read before the Geological 
Society I have described these rocks as "fossiliferous grauwacke," but 
this term is in reality a misnomer, as the group contains few if any 
