456 



HISTORICAL GEOLOGY 



addition to the Old Red Sandstone there are marine deposits contain- 

 ing abundant fossils. Volcanic action in Europe during the Devonian 

 is proved by thick volcanic accumulations in Great Britain and west 

 central Europe. 



Life of the Devonian 



The invertebrate life of this period was, in general aspect, like 

 that of the Silurian, but there were many changes in genera and an 

 almost total change in species. The contrast between the inverte- 

 brate life of the Silurian and the Devonian was about as marked as that 

 between the Ordovician and the Silurian. As in the foregoing periods, 

 certain species were characteristic not only of the period as a whole 

 but of each of its stages. 



Cceleriterata 



Corals (Fig. 428 A-C) were present in great numbers and species, 

 being almost or quite as abundant as in the Silurian. Cup corals 



(Tetracoralla, Fig. 428 

 A, C), honeycomb corals 

 (Favosites), and organ- 

 pipe corals (Syringo- 

 pora) flourished when 

 conditions were favor- 

 able, but chain corals 

 (Halysites) had be- 

 come extinct in the be- 

 ginning of the period. 



The coral-reef character 

 of some of the limestones 

 of the period is splendidly 

 exhibited at the falls of 

 the Ohio, Louisville, Ken- 

 tucky, "where the corals 

 are crowded together in 

 great numbers, some stand- 

 ing as they grew, others lying in fragments, as they were broken and heaped by the 

 waves, branching forms of large and small size mingling with massive kinds of hemi- 

 spherical and other shapes." "Some of the cup corals are 6 or 7 inches across at 

 tin top, indicating a coral animal 6 or 8 inches in diameter." "Hemispherical com- 

 pound corals occur 5 or 6 feet in diameter." "The various coral polyps of the era 

 had, beyond doubt, bright and varied colorings, like those of the existing tropics, 

 and the reefs were therefore an almost interminable flower garden." (Dana.) 



FlG. 428. — Devonian cup and compound corals: 

 ./, II rliophyllum halli; B, Pleurodictyum stylopora; C, 

 Acervularia davidsoni. 



