LAMARCK'S WORK IN GEOLOGY 53 



nitz, in his Thdorie de la Terre, published in 1749, 

 adopted his notion of an original volcanic nucleus 

 and a universal ocean, the latter as he thought leav- 

 ing the land dry by draining into subterranean cav- 

 erns. He also dimly saw, or gathered from his read- 

 ing, that the mountains and valleys were due to 

 secondary causes ; that fossiliferous strata had been 

 deposited by ocean currents, and that rivers had 

 transported materials from the highlands to the low- 

 lands. He also states that many of the fossil shells 

 which occur in Europe do not live in the adjacent 

 seas, and that there are remains of fishes and of 

 plants not now living in Europe, and which are 

 either extinct or live in more southern climates, and 

 others in tropical seas. Also that the bones and 

 teeth of elephants and of the rhinoceros and hippo- 

 potamus found in Siberia and elsewhere in northern 

 Europe and Asia indicate that these animals must 

 have lived there, though at present restricted to the 

 tropics. In his last essay, kpoques de la Nature 

 (1778), he claims that the earth's history may be 

 divided into epochs, from the earliest to the present 

 time. The first epoch was that of fluidity, of incan- 

 descence, when the earth and the planets assumed 

 their form ; the second, of cooling ; the third, when 

 the waters covered the earth, and volcanoes began 

 to be active ; the fourth, that of the retreat of the 

 seas, and the fifth the age when the elephants, the 

 hippopotamus, and other southern animals lived in 

 the regions of the north ; the sixth, when the two 

 continents, America and the old world, became sepa- 

 rate ; the seventh and last being the age of man. 



