In Silurian and Devonian Epochs 135 



So while in the seas and along the shores of that north- 

 ern region, a teeming invertebrate fauna existed, that was 

 rich in corals, echinoderms, brachiopods, and molluscs, ex- 

 tensive freshwater lakes, rivers and swamps developed and 

 sheltered myriads of phyllopod crustaceans, of eurypterids, 

 of bivalve molluscs, and specially of fishes, that attained at 

 times to huge size and formidable defensive armature. 

 While some of these like Cephalaspis, Bothriolepis and 

 Euphanerops have left no living descendants or representa- 

 tives, others belonged to elasmobranch, dipnoan, or ganoid 

 groups that are still alive in derivative types. 



Contemporaneous with these on land areas and often 

 washed into the freshwater deposits to be preserved there, 

 were scorpions, myriapods, and insects, as well as a varied 

 vegetation, many members of which had reached to a high 

 stage of lepidodendroid, equisetoid, or pteridoid organiza- 

 tion. This freshwater or land flora and fauna have been 

 made known to us, in part by preservation in or between 

 successive deposits of mud, lime, or sand that were laid 

 down during periodic freshets which affected lake, river and 

 flood-plain areas, in part by rapid deposit of volcanic dust 

 or other debris laid down during or soon after widespread 

 volcanic activity. This destroyed coi^ntless myriads of 

 organisms, not least of fishes, whose hard parts occur often 

 in "bone-beds." 



The question of mineral-oil or petroleum production 

 has already been treated (pp. 49-59), but we would here 

 emphasize that as the climax of fish-evolution in number 

 of individuals and wide community of species had now been 

 reached, so it is from these strata that the richest and most 

 valuable supplies of mineral oil have been secured in the 

 latter half of the past century. Such we would attribute 

 almost wholly to the volcanic destruction and rapid entomb- 

 ment of myriads of fishes. 



Finally before passing to the next great formation, 

 we would direct attention to the diagram of possible con- 

 tinental relations that existed during the late Devonian and 

 Carboniferous periods (Fig. 15). This sets forth details 

 that seem to be needed in explanation of the evolution and 

 distribution of ancient fishes of that time. Wide continuity 



