OF THE UNIVERSE. ROMAN EMPIRE. 189 



under the tropic or the equator upon the maximum of tem- 

 perature of the air ; he treats of the various causes of the 

 changes which the surface of the earth undergoes ; of the 

 breaking through of the boundaries of lakes or seas originally 

 closed ; of the general level of the sea (already recognised 

 by Archimedes) ; of its currents ; of the eruptions of sub- 

 marine volcanoes ; of petrifactions of shells, and impressions 

 of fishes ; and even of the oscillations of the crust of the 

 earth, which last point especially arrests our attention, as it 

 has become the nucleus of modern geology. Strabo says 

 expressly that the alterations of the boundaries between land 

 and sea are to be attributed to the rising and sinking of the 

 land rather than to small inundations ; "that not only 

 detached masses of rock, or small or large islands, but even 

 whole continents may be raised up." Like Herodotus, 

 Strabo is also attentive to the descent of nations, and to the 

 diversities of race in mankind ; he curiously enough calls 

 man a " land and air animal" who t requires much light n 

 ( 294 ). We find the ethnological distinctions of races most 

 acutely and accurately marked in the commentaries of Julius 

 Caesar, as well as in Tacitus's fine eulogium on Agricola. 



Unfortunately Strabo's great work, so rich in facts and in 

 the cosmical views which we have here referred to, remained 

 almost unknown in Eoman antiquity until the fifth century, 

 and was not even employed by the all-collecting Pliny. 

 Towards the end of the middle ages Strabo's work became 

 influential on the direction of ideas, though in a less degree 

 than the more mathematical and more dry and tabular 

 geography of Claudius Ptolemaeus, from which physical visrs 

 are almost entirely absent. This latter work became the 

 guiding clue of all travellers as late as the sixteenth century ; 



