UPPER SILURIAN. 235 



n. Life. 



The Salina beds are for the most part destitute of fossils. The 

 lower beds in New York contain a few species, imperfectly preserved ; 

 and the same is true of the upper. The latter, however, are regarded 

 as rather of the next (Lower Helderberg) period. 



III. General Observations. 



Geography. — The position of the Saliferous beds over the State of 

 New York indicates that the region, which in the preceding period was 

 covered with the sea, and alive with Corals, Crinoids, Mollusks, and 

 Trilobites, making the Niagara limestone, had now become an interior 

 shallow basin, or a series of basins, mostly shut off from the ocean, 

 where the salt waters of the sea, which were spread over the area at 

 intervals, — intervals of days, or months, or years, it may be, ■ — evap- 

 orated, and deposited their salt over the clayey bottoms. In such 

 inland basins, the earthy accumulations in progress would not consist 

 of sand or pebbles, as on an open sea-coast, but of clay or mud, such 

 as is produced through the gentle movements of confined waters. 

 Moreover, the salt waters would become, under the sun's heat, too 

 densely briny for marine life, and at times too fresh, from rains ; and 

 the muddy flat might be often exposed to the drying sun, and so be- 

 come cracked by shrinkage. The shrinkage-cracks, the clayey nature 

 of the beds, the absence of fossils, and the presence of salt, all accord 

 with this view. Salt cannot be deposited by the waters in an open 

 bay; for evaporation is necessary. The warm climate of the Silurian 

 age and the absence of great rivers were two conditions favorable for 

 such results. At some of the smaller coral islands in the Pacific, the 

 lagoon (or lake) of the interior is so shut off from free communication 

 with the ocean, as to exemplify well the above-mentioned conditions. 

 In the confined lagoon, there are often no fragments of corals or shells 

 along the shores, but, instead, a deep mud of calcareous material, made 

 out of the broken shells and corals by the triturating wavelets, — so 

 deep and adhesive that the waters of the lagoon are somewhat difficult 

 of access. This calcareous mud, if solidified, would become a non-fos- 

 siliferous limestone, like a large part of the coral rock ; and yet, a few 

 hundred yards off on the sea-coast, there ai"e other limestones forming, 

 that are full of corals and shells. In another small Pacific coral island, 

 called Baker's, there is a bed of gypsum two feet thick, attributable 

 to the evaporation of sea-water, as remarked by the describer, J. D. 

 Hague. 1 



The Saliferous flats of New York spread nearly across the State, 

 1 Am. Jour. ScL, II. xxxiv. p. 22-1. Dana's Corals and Coral Islands, pp. 182, 294. 



