Pliny (ii. 103, 104) writes:  “Itaque solis ardore siccatur liquor;…sic mari late patenti saporem incoqui salis, aut quia exhausto inde dulci tenuique, quod facillime, trahat vis ignea, omne asperius crassiusque linquatur:  ideo summa æquarum aqua dulciorem profundam:  hanc esse veriorem causam asperi saporis, quam quod mare terræ sudor sit æternus:  aut quia plurimum ex arido misceatur illi vapore, aut quia terræ natura sicut medicatas aquas inficiat.”  The first of these three theories was that of Hippocrates (De Aere, Locis, et Aquis, iv. 197) and of Anaximander (Plutarch περὶ τῶν ἀρέσκ, etc. ii. 552).  On the second vide Arist., Prob. xxiii. 30.  The idea of the sea being the earth’s sweat was that of Empedocles.  cf. Arist., Meteor. ii. 1.