M4 CONTEMPORANEOUS DEPOSITION [chae. ivi. 



(he terraces at Coquimbo (to a height of 250 feet), but are em- 

 bedded in a friable calcareous rock, which in some places is as 

 much as between twenty and thirty feet in thickness, but is of 

 little extent. These modern beda 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 continent, I found no regular strata con- 

 taining 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 

 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 explanation, 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 brouglit 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 escarp- 

 ments or ancient sea-cliflTs at different levels, one above another, 

 on that same liiie of coast. 



The old underlying tertiary formation at Coquimbo, appears 

 to be of about the same age with several deposits on the coast of 

 Chile (of which that of Navedad is the principal one), and with 

 the great formation of Patagonia. Both at Navedad and in Pa- 

 tagonia there is evidence, that since the shells (a list of which has 

 been seen by Professor E. Forbes) there intombed were living, 

 there has been a subsidence of several hundred feet, as well as 

 an ensuing elevation. It may naturally be asked, how it comes 

 that, although no extensive fossiliferous deposits of the recent 

 period, nor of any period intermediate between it and the ancient 

 tertiary epoch, have been preserved on either side of the cou- 



