44 PROF. EDWARD HULL, LL.D., F.E.S., F.G.S., ON 



plies afiorrled by the raiii and rivers are concerned, the ocean 

 waters ought apparently to be fresh rather than salt. 



2 In using the terms "fresh " and "salt" here, and in the 

 following pages, I do so in the popular sense of the words. 

 Scarcely any natural water, except rain, is absolutely free 

 from dissolved salts. All rivers contain them to a greater or 

 less extent, as do also the waters derived from wells and 

 springs. Such Avaters, however, are called . (and properly 

 called) '• fresh," which does not necessarily mean water ab- 

 solutely devoid of salts in solution ; but when the proportion 

 of salts is so great as to cause the water in Avhich they are 

 dissolved to appear " salt " to the taste, then the term salt 

 Avater or brine is applied to them. The varieties of saline 

 waters and the degrees of salinity are innumerable, and their 

 properties and uses vary accordingly. There are the salt 

 waters of the Dead Sea — so acrid as to be nauseous to the 

 taste ; there are those of the ocean, not so acrid : there are 

 the varieties of mineral waters, and the brine springs highly 

 impregnated Avith sodium chloride. But it is not necessary 

 to go further into this branch of the subject; all that is 

 necessary is to understand clearly the meaning of the terms 

 Ave employ, and in the following essay I shall use the Avords 

 fresh, brackish, and salt as applied to Avater in the sense they 

 are popularly understood. 



3 But before entering upon the discussion regarding the 

 cause or origin of the saltness of the oceanic Avaters Ave may 

 endeaA'our to ascertain whether this highly saline character 

 has characterised these Avaters throughout a very long period 

 of geological time. Now the evidence we can safely rely 

 upon in this part of our enquiry is mainly derived from the 

 character and affinities of the organic forms of past geological 

 ages. At the present day the molluscan and other forms 

 Avhich inhabit the ocean Avaters are distinguishable from 

 those Avhich inhabit fresh water lakes and riA^ers, Avhile there 

 are numerous others, such as the Actinozoa or corals, star- 

 fishes, crinoids, sea-urchins, and echinoderms, exclusiA'-ely 

 confined to oceanic Avaters at the present day. Amongst the 

 molluscs the Brachiopods (molluscoidea) and the Cephalopods 

 are specially characteristic of oceanic AA^aters of the present 

 day, and are therefore of special value in the attempt to 

 determine the character of the Avaters which they inhabited in 

 past geological times. 



4 NoAv representatives of all these forms are found not only 

 in Tertiary, Secondary, but CA'en in early Primary or 



