166 Notices of Memoirs—Prof. Edward Hull— 
of past geological ages. At the present day the molluscan and other 
forms which inhabit the ocean waters are distinguishable from those 
which inhabit fresh water lakes and rivers, while there are numerous 
others, such as the Actinozoa or corals, star-fishes, crinoids, sea- 
urchins, or echinoderms, exclusively confined to oceanic waters at 
the present day. The Brachiopods and the Cephalopods are 
specially characteristic of oceanic waters of the present day, and 
are therefore of special value in the attempt to determine the 
character of the waters which they inhabited in past geological 
times. 
4, Now representatives of all these forms are found not only in 
Tertiary and Secondary, but even in early Primary or Palzeozoic strata. 
Not only in the Cretaceous and the Jurassic strata, but also in the 
Carboniferous, Devonian, Silurian, Ordovician and Cambrian forma- 
tions do we find corals, crinoids, starfishes, sea-urchins, various forms 
of Brachiopods and Cephalopods, differing indeed specifically from, 
but sometimes generically related to, those of the present day. ‘The 
forms which are thus preserved to us in a fossil state are only those 
which were furnished with a steny or horny skeleton or integu- 
ment. Many other forms there were which had no calcareous 
skeleton, and consequently have not been preserved in a fossil 
state, but which are represented in 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 were 
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 salinity of existing 
ocean waters were possibly represented by others capable of sus- 
taining 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, etc., 
are capable of surviving in the Baltic, or of ascending estuaries, 
where 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 environment 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 Hurope, 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 matter 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 portions of the ocean have been cut off from the main 
_mass and the salts have been deposited as the waters have decreased 
