100 NORTHERN CHILE. 



plains; in some parts there are six of them, but 

 generally only five ; they run up the valley for thir- 

 ty-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 small- 

 er scale, those great ones along the whole coast- 

 line of Patagonia. They have undoubtedly been 

 formed by the denuding 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 surface of the terraces at Coquimbo (to a height 

 of 250 feet), but are embedded in a friable calcare- 

 ous rock, which in some places is as much as be- 

 tween twenty and thirty feet in thickness, but is of 

 little extent. These modern beds rest on an an- 

 cient tertiary formation containing shells, apparent- 

 ly all extinct. Although I examined so many 

 hundred miles of coast on the Pacific, as well as 

 Atlantic side of the continent, I found no regular 

 strata containing sea-shells of recent species, ex- 

 cepting 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 fossiliferous 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 ex- 

 planation, 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 ex- 

 posed to the wearing action of the sea-beach ; and 



