SALTER AND AVELINE ON THE CARADOC SANDSTONE. 73 



Caradoc sandstone are now divided into two groups. The lowest and 

 greatest portion is equivalent to the middle and upper portions of the 

 Llandeilo and Bala rocks, and were accumulated in the following 

 order : — 

 1. Fine shales, with small Trilobites {Olemis, Jsaphus, Agnostus) 



and shells, deposited in deep water (most probably the equivalents 



of the Black Shales, Malvern). 



Elevation of Land, or Shallowing of Sea. 



2. Coarse calcareous grits and conglomerate ; a littoral or shallow 

 water deposit. 



3, 4. Sandstones, with occasional pebbles, laminated in the upper 

 parts, and in some localities northwards with many beds of shale. 

 A finer deposit than the last, and indicating a greater depth of 

 water. Fossils exactly those of Bala. 



5. Thin-bedded arenaceous shales, with fewer fossils, but of the same 

 species ; Trinucleus concentricus very abundant. A still greater 

 depth of water is here indicated. (The higher part of the Llan- 

 deilo or Bala series.) 



Evidence of upheaval and partial dislocation. 



6. A coarse deposit (unconformable on Nos. 1 to 5) in the imme-- 

 diate neighbourhood of the Longmynds, and derived from them 

 (in part deep water around steep land, Forbes). A great change 

 in the organic remains. The characteristic Llandeilo and Bala 

 fossils have given place to a mixed series, including several species 

 found in the Upper Llandeilo flags, but with many others more 

 characteristic of the Wenlock lirnestone. 



7. Finer sandstones, with much shale and great abundance of Pe7i- 

 tameri, and other Brachiopoda. Land gradually sinking Qiamsay, 

 Geol. Journ. vol. ix. p. 175). Fossils chiefly Upper Silurian. 



8. 9. Grey and greenish shales, very fine sediment: deep water. 

 Trilobites, Graptolites, and Cephalopods abundant. Fossils all 

 Upper Silurian. 



Appendix. 



Desaiption of some of the Fossils. By J. W. Salter, Esq. F.G.S. 



Some of the most characteristic fossils mentioned in the above 

 lists are yet unpublished ; it seems desirable therefore to give their 

 characters in brief. 



1. Bellerophon nodosus, Salter. 



B. ornatus, M'Coy, Syn, Woodw. Foss. 310. 



B. vix uncialis, anfractibus 3, subaugulatis, costatis. A])ertma lata, siib- 

 rhombica, facie umbilicali planata, quain cxtcriori rotuiidatti brcviore. 



