In Silurian and Devonian Epochs 99 



Now in all of the above descriptions the Lingulae are 

 said to be either broken or the shells are heaped together 

 with the fish and eurypterid remains. Such may quite well, 

 therefore, have been derived as washouts and redeposits 

 from older rocks, or may have been washed up during 

 high seas and mixed with the fishes in coastal lacustrine 

 marshes. Further light is shed on this later. 



If comparison be made of the organisms mentioned in 

 the two tables of the papers referred to above it will be 

 observed that, except for Linqula, the enclosed organisms 

 of the lower or Aymestry series are marine and are quite 

 different from those above, also that in the latter or Ludlow 

 and Temeside beds there are grouped mainly eurypterid 

 and fish remains, while Salter adds that "the plant which 

 Dr. Hooker described (Q. J. Geol. Soc. 9 (1853) 12) and 

 for which he now proposes the characteristic name Pachy- 

 theca sphaerica is the common fossil in the sandstone, and 

 accompanied as at Ludlow by plant remains and fragments 

 of Pterygotus." 



Before offering any interpretation we may take up the 

 views of more recent observers. A. S. Woodward, 

 (5(5:429) in a valuable review of the relation between 

 the Lower Old Red and Upper Silurian as illustrated in 

 the Ludlow region, strongly inclined to view the latter as 

 passage beds from Old Red lacustrine conditions above to 

 increasingly marine ones below. But he was at times 

 puzzled by the biological relationships. Thus, he says 



(P-435): 



"The passage beds in question vary in different places 



in constitution and thickness, but they all show the mingling 

 of truly marine fossils such as Lingula with the fishes and 

 eurypterids, which must have been able to live either in 

 the open sea or in lakes." Now in most of the above de- 

 scriptions the Lingulae are said to be either broken or the 

 shells lie on the surfaces of the shales, or as layers of tritu- 

 rated remains. Thus in the paper of Roberts and Randall 

 (p. 231) they specially note: (a) the abundance of Lin- 

 gulae that occur in two relations; either as well-preserved 

 shells upon the surfaces of the shales, or as layers of tritu- 

 rated shells: (b) the importance of the fish-fauna of the 



