ANNIVERSARY ADDRESS OF THE PRESIDENT. IxXVU 



d'Orbigny, and there is a great fossiliferous formation fifteen degrees 

 northward in Columbia which is considered to belong to the earlier 

 stage of the cretaceous system. "Hence/' says Mr. Darwin, "bear- 

 ing in mind the character of the few fossils from Tierra del Fuego, 

 there is some evidence that a great portion of the stratified deposits 

 of the whole vast range of the South American Cordillera belongs to 

 about the same geological epoch*." 



One of the circumstances not the least interesting connected with 

 the occurrence of these cretaceo-oolitic beds at this vast elevation, 

 and in so greatly-disturbed stratification, is the evidence they aiford 

 of the elevatory and subsiding movements to which the strata con- 

 stituting the Cordillera have been subjected. On this subject Mr. 

 Darwin makes the following observations : " It is well-worthy of 

 remark, that the shells contained in the limestone bed of the Cumbre 

 series must have been covered up, on the least computation, by 4000 

 feet of strata. Now we know from Professor Forbes' s researches, 

 that the sea at greater depths than 600 feet becomes exceedingly 

 barren of organic beings ; hence, after this limestone was deposited, 

 the bottom of the sea where the main line of the Cordillera now 

 stands, must have subsided some thousand feet, to allow of the depo- 

 sition of the superincumbent submarine strata. Without supposing 

 a movement of this kind, it would moreover be impossible to under- 

 stand the accumulation of the several lower strata of coarse well- 

 rounded conglomerates, which it is scarcely possible to believe were 

 spread out in profoundly deep water, and which, especially those 

 containing pebbles of quartz, could hardly have been rounded in 

 submarine craters, and afterwards ejected from them, as I believe to 

 have been the case with much of the porphyritic conglomerate for- 

 mation. I may add, that in Professor Forbes' s opinion, the species 

 of mollusca that have been described probably did not live at a much 

 greater depth than 20 fathoms, that is, only 120 feetf ." 



But I have yet to call your attention to other and no less remark- 

 able proofs of repeated upward and downward movements, not only 

 of this great mountain-chain, but of the whole breadth of the con- 

 tinent. All the main valleys on both flanks of the Chilian Cordillera 

 have formerly had, or still have, their bottoms filled up to a consider- 

 able thickness by a mass of rudely stratified shingle. In central 

 Chile, the greater part of this mass has been removed by the torrents ; 

 clifP-bounded fringes more or less continuous being left at corre- 

 sponduig heights on both sides of the valleys. The thickness of the 

 gravel forming these fringes ranges from 30 to 80 feet, and near 

 the mouths of the valleys it is in several places from 200 to 300 

 feet. Almost eyeiywhere the pebbles are perfectly rounded, occa- 

 sionally they are mixed with great blocks of rock, and are generally 

 distinctly stratified, often vdth parting seams of sand. The plain of 

 Uspallata on the eastern side of the Cordillera, between that great 

 range and the parallel lower range of Uspallata, at a height of 6000 

 feet above the level of the sea, with a breadth of from ten to fifteen 

 miles, and extending with an mibroken surface 180 miles, is drained 

 * Page 234. f Page 193. 



