In Roman times, this increase of subterranean excitement in the early part of the year appears to have received a supernatural interpretation. It was looked on as evidence that at that season Vulcan and his Cyclops were specially busy over their furnaces, forging the thunderbolts that the Father of Gods and men was to use during the ensuing summer. Thus Horace, when joyously enumerating to his friend L. Sextius the signs that winter is giving way to spring--the disappearance of ice and hoar-frost, the coming of the balmy west wind, the release of the cattle from their stalls and of the farmer from his fireside, the advent of the goddess of love, and the dances of the nymphs and graces under the bright moon--adds that now is the time 'When fiery Vulcan lights anew The Cyclops' glowing forge.'[14] Long before these fables had ceased to be tacitly accepted by the people, they had begun to be rejected by the more thoughtful men in the community. There slowly grew up a belief in the settled and continuous sequence of nature.[15] In the midst of the schemes that were devised for explaining the old myths or making them fit into the widening experience of later ages, we may detect the dawn of the scientific spirit. Observant men were now able to recognise that what had been regarded by their grandfathers as evidence of supernatural agency, might well have been produced by natural and familiar processes of change. The early geographers afford us some interesting illustrations of the growth of this naturalism. Thus, Herodotus, in his excellent description of the physical geography of Thessaly, takes occasion, as a man of his reverent spirit naturally would, to mention the popular belief that the striking gorge of Tempe had been rent open by a blow from the trident of Poseidon. He admits the likelihood of the explanation, but immediately proceeds to state his opinion that the formation of this defile was not an abnormal manifestation of divine power, but was to be regarded as an example of the ordinary system of the world. 'Whoever believes,' he says, 'that Poseidon causes earthquakes and rents in the earth will recognise his handiwork in the vale of Tempe. It certainly appeared to me to be quite evident that the mountains had been there torn asunder by an earthquake.'[16] Coming down some four centuries later we find that in Strabo, while all allusion to the supernatural has disappeared, the formation of the topography by natural causes is described with as much confidence as if the events were vouched for by documentary evidence. 'When the present chasm of Tempe,' he remarks, 'was opened by the shocks of an earthquake, and Ossa was torn away from Olympus, the Peneius flowed out through this passage to the sea, and thereby drained the interior of the country.'[17] He speaks also of the two lakes Nessonis and Bœbeis as remnants of the large sheet of water which had originally covered the lowlands of Thessaly.