pai-t 2] THE TALENTIAN SEBIES. 145 



The Shelly Sandstones (No. 4) are those that rise at low angles 

 from below the Lower Ludlow Kock in Shropshire, and occupy 

 separate ridges on the south-eastern flanks of the Wrekin and 

 Caer Caradoc, 



In this paper Murchison remarks (p. 476) that towards the 

 base of the Lower Ludlow Rock (3) a thin calcareous zone is 

 observ^able in Shropshire, containing Pentameriis Icevis and a new 

 species of that bivalve differing from the species (P. knightii) 

 noted in the overlying group (2), 



In the second paper (1834) he gives the following classifica- 

 tion, in which the local names of Horderley and May-Hill Kocks 

 are given to the group of Shelly Sandstones (No. 4) and local 

 names to each of the remaining groups : — 



1. Ludlow Rocks. 



2. Wenlock and Dudley Rocks. 



3. Horderley and May- Hill Rocks. 



4. Builth and Llandeilo Flags. 



5. Longmynd and Gwastaden Rocks. 



' The name of May Hill in Gloucestershire is added to that of Horderley> 

 because in that well-known hill, several members of the formation (par- 

 ticularly the red and shelly sandstone) are well exhibited.' 



On another page he remarks : — 



' May Hill, in Gloucestershire, is cited as a good type of the formation, 

 where it is also overlaid by superior deposits.' 



He observes also (p. 15) that the impure limestone at the base 

 of the Wenlock Shale, and constituting the top of the shelly 

 sandstones, is strongly marked by its peculiar character and organic 

 remains. 



The views of Murchison received fuller exposition when his 

 ' Silurian System ' appeared in 1839, and a great many fossils 

 from the various group)S were figured and described by well-known 

 palaeontologists. 



The Horderley and Ma3^-Hill Rocks there received the collective 

 name of Caradoc Sandstone, which therefore comprised the 

 rocks between the Llandeilo Flags beneath and the Wenlock Shale 

 above. 



The terms Upper and Lower Silurian were also intro- 

 duced, the former to include the Wenlock and Ludlow formations 

 and the latter the Caradoc Sandstone and Llandeilo Flags. 



The organic remains of the Caradoc Sandstone were copiously 

 illustrated and described ; but the peculiar calcareous band men- 

 tioned in his earlier papers as occurring at the base of the Wen- 

 lock, characterized by Pentamerus Icevis, etc., was now united 

 with the Caradoc Sandstone, and its fossils were described along 

 with those from that formation. This was an unfortunate step, 

 as it obscured the relation of the fauna to that of the Wenlock 

 Series, and gave a false impression of a close affinity between the 

 Lower and the Upper Silurian faunas. 



The range of these rocks along the Welsh borders and into 



