42 GEO GRA PHIC FEA TURES OF SO UTHERN PA TA G ONI A 



wall stretching far awa}' on either hand until lost in the northern 

 and soutliern horizons. This line of bluffs extends throughout the 

 entire eastern coast of Patagonia, with but occasional interruptions 

 at the mouths of the few rivers that, flowing eastward from the Andes 

 across the plains, discharge their waters into the Atlantic. 



The rocks forming the cliffs consist of alternating layers of sand- 

 stones and clays, approximately though not entirely horizontal, of a 

 prevailing light brown or gray color, and everywhere remarkably free 

 from any faults or other distur])ances. Although the color and litho- 

 logical characters of the rocks are quite similar throughout the entire 

 coast line, 3'et there is a decided difference in their age and origin, 

 as shown b}' the fossils contained in them. Toward the north the 

 entire series of strata l)elong to the Patagonian beds, of Middle Ter- 

 tiary age and marine origin, and contain in great abundance the fossil 

 remains of oysters, pectins, brachioi)ods bryozoans. etc., together 

 with occasional bones and skulls of whales, dolphins, and other ceta- 

 ceans, 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 the}^ dip very gently to the southeast, as is demonstrated 

 by the fact that the succeeding strata gradually disappear beneath 

 the waters of the Atlantic as we })roceed southward along the coast. 

 So slight, however, is this southed}^ dip that for more than 100 miles 

 only the Patagonian beds are seen in the bluffs; Init 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 materials 

 aj^pear at the summit conformably overl3nng the Patagonian beds. 



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

 lacustrine and ivolian 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 southeast, so that in the region of C03' Inlet 

 their lowermost strata have reached the water level, while the entire 

 series forming the Patagonian beds are here submerged beneath the 

 waters of the Atlantic. 



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

 tirely composed of the Santa Cruz beds. At Cape Fairweather 

 another series of rocks api)ears at the summit unconformabl}^ over- 

 Iving the Santa Cruz beds and designated as the Cape Fairweather 



