I04 LAMARCK, HIS LIFE AND WORK 



secular elevation of a continental plateau by crust- 

 movements, and Lamarck's idea of the formation of 

 elevated plains on land by the accumulation of debris 

 of organisms is manifestly inadequate, our aerial or 

 eolian rocks and loess being wind-deposits of sand 

 and silt rather than matters of organic origin. Thus 

 he cites as an example of his theory the vast elevated 

 plains of Tartary, which he thought had been dry 

 land from time immemorable, though we now know 

 that the rise took place in the quaternary or present 

 period. On the other hand, given these vast elevated 

 plains, he was correct in affirming that rivers flowing 

 through them wore out enormous valleys and carved 

 out high mountains, left standing by atmospheric 

 erosion, for examples of such are to be seen in the 

 valley of the Nile, the Colorado, the Upper Missouri, 

 etc. 



He then distinguishes between granitic or crystal- 

 line mountains, and those composed of stratified 

 rocks and volcanic mountains. 



The erosive action of rivers is thus discussed ; they 

 tend first, he says, to fill up the ocean basins, and 

 second, to make the surface of the land broken and 

 mountainous, by excavating and furrowing the plains. 



Our author did not at all understand the causes of 

 the inclination or tilting up of strata. Little close 

 observation or field work had yet been done, and the 

 rocks about Paris are but slightly if at all disturbed. 

 He attributes the dipping down of strata to the in- 

 clination of the shores of the sea, though he adds 

 that nevertheless it is often due to local subsi- 

 dences. And then he remarks that " indeed in many 



