Changes in the Belative Level of Sea and Land. 307 



and land on the western shores of the continent ; they are 

 no less conspicuous 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 be- 

 tween 300 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."* 



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

 instances, 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 sea-coast, 

 where marine shells of existing species lie near the surface 

 and upon it ; in other words, that we have that which re- 

 cently 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 Arctic Ocean, which they were the first to discover. In 

 ascending the Dwina, which flows into a bay of the Icy Sea 

 at Archangel, they discovered at about 150 miles from that 

 city, near where the Vaga, a tributary, falls into the Dwina, 

 a profusion of shells having a very modern aspect, regularly 

 imbedded in clay and sand of about ten feet in thickness, 

 which, covered by about twenty feet of the coarse gravel and 

 detritus of the country, reposed on red and white gypsum, 

 subordinate to red marls of the Permian system of rocks. 

 They traced these shelly beds to a distance of about 8 miles. 

 Some of the shells preserved in the blue clay or marine sand, 

 and thereby excluded from atmospheric influence, have re- 

 strained all the freshness of their original colour, with their 

 valves often united ; and the whole, even when blanched, are 

 generally in a good state of preservation. What they col- 



* Journal of a Voyage round the World, 2d edit, p. 171. 



