104 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 débris 
of organisms is manifestly inadequate, our aérial 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, 
GUC: 
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 
