Mr. Murchison on the Transition Rocks of Shropshire, §c. 371 



in the formation is considerable, including a new genus of Crusta- 

 ceans, another of Cephalopods, and a third of Conchifers. 



2. Wenlock and Dudley Rocks. — The coralline limestones of 

 Wenlock and Dudley having been shown to be equivalent, the term 

 of" Wenlock and Dudley rocks" has been adopted, that the name 

 of the last-mentioned place, so well-known for its organic remains, 

 may serve to mark a zone in the Geological Series. 



The lower part of this formation is termed the " Wenlock shale," 

 the local term of" Die earth," used last year, having been abandoned 

 by the author, because he finds that it has been applied by the mi- 

 ners to any stratum of the transition series upon which their coal 

 bearing measures have been deposited ; so that in one case their 

 " Die earth" is the lower shale of the Ludlow formation, in another 

 the shale beneath the Wenlock limestone. 



3. Horderley and May Hill Rocks. — This formation, consisting of 

 shelly sandstones, impure limestones, grits, &c, having been more 

 thoroughly examined, is found to contain many more organic re- 

 mains, and to be of much greater thickness than was formerly 

 supposed. 



The strata on the banks of the river Onny at Horderley, Salop, 

 are described in detail, as they present a full type of the formation. 

 The name of May Hill in Gloucestershire, is added to that of Hor- 

 derley, because in that well known hill, several members of the 

 formation (particularly the red and shelly sandstone) are well ex- 

 hibited. 



4. Builth and Llandeilo Flags. — These flags, so peculiarly marked 

 by the presence of the large Asaphus Buchii, and so fully developed 

 in Caermarthen and Brecknockshires, have this year been discovered 

 at Rorington in the west of Shropshire. 



5. Longmynd and Givastaden Rocks. — These constitute a great 

 mineral axis in Shropshire, occupying the hilly region of the Long- 

 mynd, Linley, the btiper Stones, c\c. ; extending to the north-east 

 in Lythand Haughmond Hills, and throwing off upon their vertical 

 flanks, the overlying formations. 



These rocks are again found in the same geological horizon at 

 Gwastaden in Brecknockshire, and also west of Llandovery inCaer- 

 marthenshire, where the siliceous and gritty members are frequently 

 in the form of concretions. The whole of this vast system (No. 5) 

 is void of organic remains. 



Each of the four fossiliferous formations above enumerated, is 

 distinguishable by an individuality of character of the organic re- 

 mains, by lithological structure, and by geographical boundaries ; 

 whilst the underlying slaty and conglomeritic system is perfectly 

 dissimilar in aspect and composition from any of the overlying 

 groups. These distinctions arc explained in the annexed Table. 

 The author however states, that in Brecknock and Caemiartlicn- 

 shins it is very difficult to draw those neat lines of separation be- 

 tween these formationgj which nature lias established in Salop, He- 

 refordshire, &c. ; and the calcareous members being almost entirely 

 absent in South Wales, it is only in certain places that these subdi- 

 3 B'J 



