194 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



are much broader, and may be called plains, and they run up the 

 valley for thirty-seven miles from the coast. Shells of many exist- 

 ing species not only lie on the surface of the terraces, to a height of 

 250 feet, but are imbedded in a friable calcareous rock, which is in 

 some places as much as from twenty to thirty feet in thickness ; and 

 these modern beds rest on an ancient tertiary formation, containing 

 shells apparently all extinct. " The explanation of the formation of 

 these terraces must be sought for, no doubt, in the fact, that the 

 whole southern part of the continent has been for a long time slowly 

 rising, and therefore that all matter deposited along shore in 

 shallow water must have been soon brought up and slowly exposed 

 to the wearing action of the sea-beach*." He describes a great val- 

 ley near Copiapo, reaching far inland, the bottom of which, consist- 

 ing of shingle, is smooth and level ; and states that he has little doubt 

 that this valley was left, in the state in which it is now seen, by the 

 waves of the sea, as the land slowly rosef. He then goes on to 

 state, "I have convincing proofs that this part of the continent of 

 South America has been elevated near the coast at least from 400 

 to 500, and in some parts from 1000 to 1300 feet, since the epoch 

 of existing shells :j:." Speaking of the neighbourhood of Valparaiso 

 he says, " The proofs of the elevation of this whole line of coast are 

 unequivocal : at the height of a few hundred feet old-looking shells 

 are numerous, and I found some at 1300 feet. These shells either 

 lie loose on the surface, or are imbedded in a reddish-black vege- 

 table mould. I was much surprised to find, under the microscope, 

 that this vegetable mould is really marine mud, full of minute par- 

 ticles of organic bodies §." 



So far for instances of changes in the relative level of sea and 

 land on the western shores of the continent ; they are no less con- 

 spicuous on the Atlantic side. " The land from the Rio Plata to 

 Tierra del Fuego, a distance of 1200 miles, has been raised in mass 

 (and in Patagonia to a height of between ^00 and 400 feet) within 

 the period of now existing sea-shells. The old and weathered shells 

 left on the surface of the upraised plain still partially retain their 

 colours. The uprising movement has been interrupted by at least 

 eight long periods of rest, during which the sea ate deeply back 

 into the land, forming at successive levels the long lines of cliffs or 

 escarpments which separate the different plains, as they rise like 

 steps one behind the other |1 ." 



Now it is important to observe, that in some of the above in- 

 stances, and also in others which Mr. Darwin gives, the proofs of 

 change are not in terraces or raised beaches only, but that there are 

 broad expanses of land far from the coast, where marine shells of 

 existing species lie near the surface and upon it ; in other words, 

 that we have that which recently was a sea-bottom now forming an 

 elevated part of the continent. 



The authors of the ' Geology of Russia ' have described a sea- 

 bottom, extending nearly 200 miles inland from the shores of the 



* Journal of a Voyage round the World, 2nd edit. p. 344. f Ibid. 355. 



+ Ibid. 357. § Ibid. 254. || Ibid. 171. 



