LAMARCK’S WORK IN GEOLOGY 93 
nitz, in his 7kéorte de la Terre, published in 1740, 
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, Epogues 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. 
