chap. xin. Patagonia, 435 



unusual on this side of the continent, of 3,340 feet. It 

 consists up to its summit, of quartz, generally pure and 

 white, but sometimes reddish, and divided into thick 

 laminaa or strata : in one part there is a little glossy 

 clay-slate with a tortuous cleavage. The thick layers 

 of quartz strike in a W. 30° N. line, dipping southerly 

 at an angle of 45° and upwards. The principal line of 

 mountains, with some quite subordinate parallel ridges, 

 range about W. 45° N. : but at their SE. termination, 

 only W. 25° N. This Sierra is said to extend between 

 twenty and thirty leagues into the interior. 



Patagonia. — With the exception perhaps of the 

 hill of S. Autonio (600 feet high) in the Gulf of S. 

 Matias, which has never been visited by a geologist, 

 crystalline rocks are not met with on the coast of Pata- 

 gonia for a space of 380 miles south of the S. Ventana. 

 At this point (lat. 43° 50'), at Points Union and Tombo, 

 plutonic rocks are said to appear, and are found, at 

 rather wide intervals, beneath the Patagonian tertiary 

 formation for a space of about 300 miles southward, to 

 near Bird Island, in lat. 48° 56'. Judging from speci- 

 mens kindly collected for me by Mr. Stokes, the pre- 

 vailing rock at Ports St. Elena, Camerones, Malaspina, 

 and as far south as the Paps of Pineda, is a purplish- 

 pink or brownish claystone porphyry, sometimes la- 

 minated, sometimes slightly vesicular, with crystals of 

 opaque feldspar and with a few grains of quartz ; hence 

 these porphyries resemble those immediately to be de- 

 scribed at Port Desire, and likewise a series which I have 

 seen from P. Alegre on the southern confines of Brazil. 

 This porphyritic formation further resembles in a 

 singularly close manner the lowest stratified formation 

 of the Cordillera of Chile, which, as we shall hereafter 

 see, has a vast range, and attains a great thickness. 

 At the bottom of the Gulf of St. George, only tertiary 



