AGE OF MOLLUSKS. 193 



shores of the present day. "Unstable as water" is a 

 proverb, the truth of which has been recognized from 

 time immemorial ; but the water, though itself unstable, 

 lias left stable evidences of its work every where in the 

 earth. It has left traces in rock which have lasted ages 

 upon ages longer than any chiselings of man upon mon- 

 umental granite. 



281. Life in this Age. As the beach-arrangement of 

 land was prominent, so, as Agassiz remarks, the life was 

 mostly such as we find now on beaches. Mollusks were 

 abundant ; crustaceans of some kinds also, and star-fish- 

 es, sea-urchins, etc. There were corals, also, when and 

 where the circumstances were favorable to their growth. 

 I will cite two instances in contrast in this respect. In 

 forming the limestone floor of the great New York ba- 

 sins preparatory to the salt-making ( 278), the work 

 was done by coral animals, and other allied animals, as is 

 shown by the abundance of their remains in that rock. 

 But when the salt-beds came to be laid down these ani- 

 mals were absent, for the water was too salt for them to 

 live in, and few fossils are therefore found in these beds. 

 The same contrast was seen in the coral island observed 

 by Professor Dana. In the salt water of the lagoon 

 there were no corals nor shells, though there was a plen- 

 ty of them outside of the island in the open sea. There 

 were no insects in the Silurian age, and but few fishes ; 

 some think absolutely none. There were no land nor 

 fresh-water animals. As to vegetation, we have remains 

 only of the lowest forms of vegetation, such as sea-weeds 

 and club-mosses. No land-plants have been found ex- 

 cept in the uppermost strata. What life there was in 

 this age was very abundant during most of the period in 

 most localities. There was such a profusion, says Agas- 

 siz, " that it would seem as if God, in the joy of creation, 

 had compensated himself for a less variety of forms in 

 the greater richness of the early types." 



282. Adaptation. The life on the earth at that time, 



I 



