202 PALEOZOIC TIME — LOWER SILURIAN. 



Another supposition is this : that the continent may have had its 

 borders so raised that the interior was a salt-water sea, shut off from 

 the ocean, and here the waters — more calcareous in that period 

 than now — deposited the limestone ; and that new accessions of 

 calcareous material might have been received either through occa- 

 sional incursions of the ocean, or through streams flowing from the 

 land. A rock thus made, supposing the method possible, might be 

 much like the Silurian limestone in compactness and texture. 



3. Climate. — No marked difference between the life of the Pri- 

 mordial rocks in warm and cold latitudes has been observed ; and 

 there is wanting, therefore, all evidence of a diversity of climate 

 and of oceanic temperature over the earth's surface. With a warm 

 and equable climate, the atmosphere would have been moist and 

 the skies much clouded, but storms would have been less frequent 

 or violent than now. The eyes of the Trilobite, as Buckland ob- 

 serves, indicate that there was the full light of day, and therefore 

 that sunshine alternated with the clouds as now. 



4. Life. — (a.) Grades of life. — The system of life began (1) with 

 marine species ; (2) with species of three sub-kingdoms, those 

 of Radiates, Mollusks, and Articulates; but (3) with the inferior 

 species in each : the Sertularids being the lower Acalephs ; Crinoids 

 the lower Echinoderms ; Brachiopods the lower Mollusks ; and 

 Lingula and Orthis among the lower Brachiopods ; Gasteropods 

 (Univalves) with an entire aperture to the shell, the lower of Grastero- 

 podan Mollusks ; Orthocerata, or the straight-shelled Cephalopods 

 with plain septa, the lower of Cephalopodan Mollusks ; marine 

 worms, the inferior group of Articulates ; Trilobites, Phyllopods, 

 and Cyprids among the lower of Crustaceans ; and Paradoxides and 

 the associated genera of Trilobites among the lowest of the group 

 of Trilobites. None of the genera of ornamented modern sea-shells 

 have been observed, and none of those having a beaked aperture 

 to the shell ; no land or fresh-water shells ; no shrimps, lobsters, or 

 crabs (Macrourans or Brachyurans) ; no insects ; no relics of fishes, 

 reptiles, or mammals. 



While, however, the species were inferior species in the tribes 

 represented, they were not necessarily the very lowest. For Polyps 

 are, as a class, the lowest of Radiates, and yet it is not certain that 

 any Polyp-corals were in the Primordial fauna, — none being re- 

 ported from the European Primordial period, and those so called 

 found in the American rocks being probably Sponges. Trilobites, 

 although belonging to the inferior of the grand divisions of Crusta- 

 ceans, the Entomostracans, stand at the head of that division, if 

 not intermediate between them and the Tetradecapods, the next 



