In Silurian and Devonian Epochs 127 



ditions. When further a bone-bed occurs just above, that is 

 "a six-inch layer" and is crowded with fish remains, we 

 would again claim that this represents a sudden volcanic 

 dust deposit, that killed and in a few days entombed the 

 surrounding fishes over hundreds of miles. This again 

 was succeeded by a blue limestone that closely resembles 

 freshwater limestones of Europe. Orton says of this: "the 

 fossils of the Delaware beds are at this point chiefly fish- 

 remains. Teeth, plates, jaws and other bones are not un- 

 frequently met with throughout 25 ft. of this series." But 

 he does not account for the great abundance of these, nor 

 for the total absence of undoubted marine organisms, if 

 the deposit was laid down in "an ancient sea." 



It would be a premature task as yet to attempt any 

 correlation of the deposits as treated by Orton and others. 

 The palaeontological researches however of Hall, New- 

 berry, Dawson, Claypole, Clarke, Whiteaves, Matthew, 

 Traquair and Eastman, indicate three fairly sharply-marked 

 groups of freshwater strata, intercalated between others 

 that are marine. 



The lowermost beds of the formation in the central 

 Eastern States, consist of the Helderbergian and Oriska- 

 nian. These are wholly of the marine type, and yield an 

 abundant invertebrate marine fauna, though no marine fish 

 remains, where accurate record of beds has been made. 

 But probably deposited synchronously with them, though 

 in freshwater areas, are the Canadian beds, that are often 

 called the Gaspe and Campbellton. The included fishes are, 

 in their affinities, a curious blending of the European Upper 

 Silurian and Lower Old Red. Thus there are abundant 

 examples of Thelodus (Fig. 8a), several species of CepJial- 

 aspis (Fig. 9a), and from the lower-most beds Asterolepis 

 clarkei, all of these being of Silurian-Devonian age and of 

 agnathous structure. 



But with them are Acanthodes semistriatiis and Cltmat- 

 ius latispinosus representing primitive selachians; spines 

 of the probably allied selachians Homacanthus and Macha- 

 eracanthus, the arthrodire Phlyctaenaspis acadica — a close 

 ally of Coccosteus — and isolated teeth of Dendrodus. 



