20 HISTORY OF THE SCIENCE. 



cause to the ground, either to that portion which is under 

 the sea, or to that which is covered by it ; and rather to 

 the latter, from its being rendered more movable by mois- 

 ture, and susceptible of greater change." He continues, 

 " The real cause, I repeat, of all these changes is, that the 

 bed of the sea is sometimes accidentally elevated, and some- 

 times depressed." 



He subsequently enforces the necessity of consulting the 

 existing phenomena of nature, with the view to explain the 

 past, " such," he observes, "as are daily occurring to our 

 observation the deluges, earthquakes, and elevations or 

 depressions of the bed of the sea ; these are the causes of 

 the rise or lowering of the waters." He adds, that as expe- 

 rience shows that not only small islets, but islands, and even 

 parts of continents, are raised from the deep, so they may 

 again be engulfed beneath the ocean. 



Lucretius, the contemporary of Julius Caesar, in his 

 poem De Nature Rerum* among a mass of theories and 

 vague speculations, states several facts of importance. He 

 attributes the formation of the earth, the seas, and the 

 atmosphere to the union of elementary atoms, impelled 

 by the laws of affinity ; and though destitute of any positive 

 acquaintance with palaeontology or botany, says, that before 

 men and existing objects lived, the earth had produced beings 

 of extraordinary form, and vegetables of enormous size. 



Ovid, in the celebrated passage of the 15th book of his 

 Metamorphoses, while illustrating the system of Pythagoras 

 and explaining the law of universal change, affords proof of 

 an acquaintance with geological phenomena, comprising, in 

 fact, a summary of almost all the causes now in operation on 

 the earth. They are so lucidly stated and explained by Sir 

 C. Lyell,t that the reader is referred to his excellent work 

 for more details, a selection of the most important being 

 sufficient for our purpose. Among the most striking are 



The conversion of land to sea, and sea to land. 



The occurrence of marine shells at a distance from the 

 ocean. 



The excavation of level plains into valleys, and the de- 

 struction of hills, and removal of their detritus into the sea. 



* Book v. f See the Introduction to his Principles of Geology. 



