250 PALAEOZOIC TIME — UPPER SILURIAN. 



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 the rains ; and the muddy flat might be often exposed 

 to the drying sun, and so become 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 can- 

 not 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 

 one small coral island in the Pacific, visited by the author, the 

 lagoon (or lake) which formed the interior was shut off from free 

 communication with the ocean, and consequently some of the 

 above-mentioned conditions were well exemplified. The waters 

 became extremely salt in the hot season, and fresh in the rainy 

 months ; and hence no living corals or shells existed there, 

 although once abundant. Moreover, while the rock was of coral 

 origin, there were no fragments of corals or shells along the shores 

 of this lagoon, but, instead, a deep mud of calcareous material, 

 made out of the broken shells and corals by the triturating wave- 

 lets, — so deep and adhesive that the waters of the lagoon were 

 somewhat difficult of access. This calcareous mud, if solidified, 

 would become a non-fossiliferous limestone, like a large part of 

 the coral rock ; and yet a few hundred yards off on the sea-coast 

 there were other limestones forming, that were full of corals and 

 shells. 



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

 probably opened on the ocean to the southeast. The existence of 

 such interior evaporating flats implies intermittent incursions of 

 the sea, perhaps only through tidal overflows, but probably such 

 occasional floodings as may take place where there are coast-bar- 

 riers or reefs that are broken through at times by the waves or 

 currents. 



The existence of such barriers is no unreasonable assumption ; 

 for the coast of the United States is now to a great extent bordered 

 with them. They stretch along the south side of Long Island, 

 shutting in a narrow area of salt water ; and south of New York 

 they occur off New Jersey, Maryland, Virginia, and the Carolinas, 

 making the various sounds that are so characteristic of the coast- 

 region. 



As the Saliferous beds of New York are nearly 1000 feet thick 

 just west of the centre of the State, and since there is proof in the 



