HOW THE WATERS OF THE OCEAN BECAME SALT. 45 



Palaeozoic strata. Not only in the Cretaceous and the 

 Jurassic strata, bnt also in the Carboniferous, Devonian, and 

 Lower Silurian (Ordovician) formations do we find corals, 

 crinoids, starfishes, sea-urchins, various forms of Brachiopods 

 and Cephalopods, differing indeed specifically from, but some- 

 times geuerically related to, those of the present day. The 

 forms which are thus preserved to us in a fossil state are 

 only those which Avere furnished with a stony or horny 

 skeleton or integument. Many other forms there were 

 which had no calcareous skeleton, and consequently have 

 not been preserved in a fossil state, but which are represented 

 iu the ocean waters of the present day; and if these be 

 allowed for, it becomes clear that amongst the invertebrate 

 forms of marine life, those of the present day w^ere largely 

 represented in very early geological periods. 



5 Such being the case we are justified in coming to the 

 conclusion that the waters of the ocean must have been salt 

 from very .early geological times ; but it by no means follows 

 that they were fully as saline as those of the present day. 



The forms of life which require the high sahnity of ex- 

 isting ocean waters were possibly represented by others 

 capable of sustaining life when the salinity was only half as 

 great as it is now. We know that some forms, such as those 

 of the oyster, cockle, &c., are capable of surviving in the 

 Baltic, or of ascending estuaries, wdiere the water is almost 

 brackish. Degrees of temperature, purity (or freedom 

 from sediment), and other conditions were probably of 

 greater importance in determining the existence of life than 

 degrees of salinity. Adaptability to the conditions of environ- 

 ment has doubtless been a law of nature amongst marine 

 forms as well as those of the air and the land throughout all 

 past time. 



6 It is scarcely necessary to state here that the occurrence 

 of beds of rock salt in several formations, especially in the 

 Trias of the British Isles and of Europe, affords no evidence 

 as regards the degree of salinity of the sea water in 

 geological times. At no period have the waters of the 

 ocean been so saturated with saline matters as to admit of 

 the deposition of beds of rock salt. It has sometimes been 

 suggested that such deposits may have been formed by the 

 accidental accumulation of sand bars, owing to which por- 

 tions of the ocean have been cut off from the main mass and 

 the salts have been deposited as the waters have decreased 

 and become supersaturated b.y evaporation. But the mode of 



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