INTRODUCTION. 9 



theories of mountain-making, and we owe to him, moreover, 

 the hypothesis that volcanic outbursts act as safety-valves for 

 the pent-up activities of subterranean vapours. He pointed out, 

 that Sicily in his time was less frequently disturbed by earth- 

 quakes than it had been in previous ages before volcanic 

 discharges were known in the district, and he correlated the 

 comparative tranquillity of the ground with the means of 

 escape afforded for explosive underground vapours by the 

 volcanic vents that had opened at Etna, in the Lipari Isles, and 

 in Ischia. It speaks highly for Strabo's powers of observation 

 that he should have recognised in Vesuvius a volcanic moun- 

 tain although it was then quiescent. 



Probably the most acute scientific observer of Roman times 

 was Seneca, the physician of the Emperor Nero (born 2 or 4 

 B.C., died 65 A.D.). Quite recently, Nehring has placed 

 the importance of the work of Seneca in its true light. The 

 Qucestiones Naturales contain detailed communications about 

 earthquakes, volcanoes, and the constructive and destructive 

 agencies of water. Seneca explains earthquakes partly as a 

 result of the expansion of gases accumulated in the earth, 

 partly by the collapse of subterranean cavities. He regards 

 volcanic eruptions simply as an intensified form of the same 

 series of phenomena, and volcanoes themselves as canals or 

 vents between local sub-terrestrial reservoirs of molten material 

 and the earth's surface. He names the chief volcanoes, 

 placing Etna in the first rank ; then Stromboli, Therasia, and 

 Thera (the present "Santorin"), but there is no mention of 

 Vesuvius. He regards the earth as primitively a watery chaps, 

 and it is more especially in his treatment of the action of water 

 in dissolving and carrying away rock-material, together with 

 his explanation of the origin of sediments and deltas, that 

 Seneca has shown his remarkable insight and sound judg- 

 ment. 



The learned historian, Pliny the Elder (23-79 A.D.), has 

 handed down to us a compendium that embraces the whole 

 scientific knowledge of antiquity. His Historia Naluralis^ in 

 thirty-seven books, embraces the natural history of animals, 

 plants, and stones, the history of the heavens and the earth, 

 of medicine, of commerce, of navigation, etc.; in Lib.. II., 

 c. 88 and 89, all the islands that have been thrown up in the 

 ocean are enumerated Delos, Rhodes, Anaphe, Nea, Alone, 

 Thera, Therasia, Hiera, Automate, and Thia. The reports 



