364 CHARLES DARWIN 



nomenon is displayed on a much grander scale, so as to 

 strike with surprise even some of the inhabitants. The ter- 

 races are there much broader, and may be called plains; in 

 some parts there are six of them, but generally only five; 

 they run up the valley for thirty-seven miles from the coast. 

 These step-formed terraces or fringes closely resemble those 

 in the valley of S. Cruz, and, except in being on a smaller 

 scale, those great ones along the whole coast-line of Pata- 

 gonia. They have undoubtedly been formed by the denud- 

 ing power of the sea, during long periods of rest in the 

 gradual elevation of the continent. 



Shells of many existing species not only lie on the sur- 

 face of the terraces at Coquimbo (to a height of 250 feet), 

 but are embedded in a friable calcareous rock, which in some 

 places is as much as between twenty and thirty feet in thick- 

 ness, but is of little extent. These modern beds rest on an 

 ancient tertiary formation containing shells, apparently all 

 extinct. Although I examined so many hundred miles of 

 coast on the Pacific, as well as Atlantic side of the conti- 

 nent, I found no regular strata containing sea-shells of 

 recent species, excepting at this place, and at a few points 

 northward on the road to Guasco. This fact appears to me 

 highly remarkable ; for the explanation generally given by 

 geologists, of the absence in any district of stratified fossil- 

 iferous deposits of a given period, namely, that the surface 

 then existed as dry land, is not here applicable; for we 

 know from the shells strewed on the surface and embedded 

 in loose sand or mould, that the land for thousands of miles 

 along both coasts has lately been submerged. The explana- 

 tion, no doubt, must be sought 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 ; 

 and it is only in comparatively shallow water that the greater 

 number of marine organic beings can flourish, and in such 

 water it is obviously impossible that strata of any great 

 thickness can accumulate. To show the vast power of the 

 wearing action of sea-beaches, we need only appeal to the 

 great cliffs along the present coast of Patagonia, and to the 



