272 PALAEOZOIC TIME — DEVONIAN AGE. 



2. Animals. 



The Upper Helderberg period is eminently the coral-reef period 

 of the Palaeozoic ages. Many of the rocks abound in corals (see figs. 

 445-451), and are as truly coral reefs as the modern reefs of the 

 Pacific. The corals are sometimes standing in the rocks in the 

 position they had when growing ; others are lying in fragments as 

 they were broken and heaped up by the waves ; and others were 

 reduced to a compact limestone by the finer trituration before con- 

 solidation into rock. This compact variety is the most common 

 kind among the coral-reef rocks of the present seas ; and it often 

 contains but few distinct fossils, although formed in waters that 

 abounded in life. At the Falls of the Ohio, near Louisville, there is 

 a magnificent display of the old reef. Hemispherical Favosites five 

 or six feet in diameter lie there nearly as perfect as when they were 

 covered with their flower-like polyps ; and, besides these, there are 

 various branching corals, and a profusion of Cyathophylla, or cup- 

 corals ; some of the species of the latter (fig. 445) have a breadth of 

 three inches, and one of six or seven inches ; and when alive the 

 expanded polyp must have had at least this diameter, or, with the 

 expanded tentacles, probably an inch or two more. These ancient 

 corals may have had the same rich and varied colors that charac- 

 terize the Zoophytes of our own epoch. 



There is another point in which the Corniferous period stands out 

 prominently in American Palaeozoic history. It contains the earliest 

 remains, thus far discovered, of fishes, — the first of the sub-kingdom of Verte- 

 brates. The life of the American seas from this time, therefore, in- 

 cluded species of all four sub-kingdoms, Radiates, Mollusks, Articulates, 

 and the branch now added, Vertebrates. 



Among Brachiopods the new genus Productus makes its first ap- 

 pearance, one that afterwards in the Carboniferous age became very 

 common : its earliest species are but half an inch in breadth, while 

 some of the later are three or four inches. Figs. 228, 229, page 183, 

 represent different species, but not those of this period. 



The hornstone contains spicula of Sponges, two of which are 

 figured in 441 A j, k; k is magnified 75 diameters. Along with 

 these, White has detected a fragment of the dental apparatus of a 

 Gasteropod, represented in fig. o. Fig. p is from a specimen of 

 this kind observed in hornstone of the Black Eiver limestone 

 (Trenton period), Watertown, N.Y., by Bradley ; Desmids and 

 spicula of Sponges accompany it. The organic origin of the Palaeo- 

 zoic hornstone can hardly be doubted. 



