S$o CONTEMPORANEOUS DEPOSITION [CHAP. no. 



These step-formed terraces or fringes closely resemble those in the 

 valley of San Cruz, and except in being on a smaller 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 calcareous rock, which in some places is as much as between 

 twenty and thirty feet in thickness, 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 continent, 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 

 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 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 thick- 

 ness 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 escarpments or ancient sea-cliffs 

 at different levels, one above another, on that same line 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 forma- 

 tion of Patagonia. Both at Navedad and at Patagonia 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 con- 

 tinent, yet that at this ancient tertiary epoch, sedimentary matter 

 containing fossil remains, should have been deposited and preserved 

 at different points in north and south lines, over a space of 1,100 miles 

 on the shores of the Pacific, and of at least 1,350 miles on the shores 

 of the Atlantic, and in an east and west line of 700 miles across the 

 widest part of the continent ? I believe the explanation is not difficult, 

 and that it is perhaps applicable to nearly analogous facts observed in 

 Other quarters of the world. Considering tlift enormous power cf 



