SUMMARY. 285 



the rocks are quite similar along the entire coast line, yet there is a de- 

 cided difference in their age and origin, as is shown by the fossils con- 

 tained in them. Toward the north the entire series of strata belongs to 

 the Patagonian beds, of Middle Tertiary age and marine origin, and con- 

 tains in great abundance the fossil remains of oysters, pectens, brachiopods, 

 bryozoans, etc., together with occasional bones and skulls of whales, 

 dolphins, and other cetaceans, all bearing unimpeachable evidence as to 

 their marine nature. 



These marine beds attain their maximum development in the region of 

 San Julian, where they show a thickness of 900 feet. From this point 

 they dip very gently to the southeast, as is demonstrated by the fact that the 

 succeeding strata gradually disappear beneath the waters of the AUantic, as 

 we proceed southward along the coast. So slight, however, is this southerly 

 dip that for more than 100 miles only the Patagonian beds are seen in the 

 bluffs ; but at a point about 40 miles south of the Santa Cruz River a second 

 series of rocks, of somewhat lighter color and composed of usually softer ma- 

 terials, appears at the summit, conformably overlying the Patagonian beds. 



This second series of strata constitutes the Santa Cruz beds, of lacus- 

 trine and asolian origin. It contains the remains of that rich and unique 

 assemblage of fossil birds and mammals, concerning the age and relations 

 of which there has been such wide discussion. Continuing southward 

 along the coast the rocks of the Santa Cruz beds dip gently to the south- 

 east, so that in the region of Coy Inlet their lowermost strata have reached 

 the water level, while the entire series forming the Patagonian beds is 

 here submerged beneath the waters of the Atlantic. 



South of Coy Inlet, as far as Cape Fairweather, the bluffs are entirely 

 composed of the Santa Cruz beds. At Cape Fairweather another series 

 of rocks appears at the summit, unconformably overlying the Santa Cruz 

 beds and designated as the Cape Fairweather beds. They are of marine 

 origin and contain, in great abundance, the remains of marine inverte- 

 brates. I should also add that throughout the entire extent of this coast 

 the uppermost crest of the bluffs is composed of from twenty to thirty feet 

 of unstratified bowlders and clays, constituting the great Shingle formation 

 of Patagonia, distributed somewhat uniformly over almost the entire sur- 

 face, and of combined ice and aqueous origin. 



From the coast a broad, elevated plain, stretches westward to the base 

 of the Andes. Its surface, abruptly terminated on the east, as we have 



