684 R- ^- F. PENROSE, JR. 



locally known as "the island," in distinction from the others. In the 

 present paper the name Tierra del Fuego will be used to indicate the 

 whole archipelago, and, as thus defined, it consists of one large island 

 and many smaller ones. It comprises an area extending about 500 

 miles in a direction from northwest to southeast and about 200 miles 

 in a direction from northeast to southwest, and from about 52° 30' 

 to almost 56° south latitude. The two main tidewater channels are 

 the Strait of Magellan on the north and Beagle Channel near the 

 southern part, intersecting the region from east to west. Between 

 these two, and also south of Beagle Channel, are numerous other 

 minor and transverse channels, dividing the archipelago into the 

 many islands of which it is composed. (See map.) 



GEOLOGY AND TOPOGRAPHY OF THE REGION 



The western part of Patagonia is comprised in the main range of 

 the Andes, dropping off abruptly on the Pacific side, while the eastern 

 part is comprised in the low rolling country known as the pampas, 

 sloping gradually to the Atlantic. South of the Strait of Magellan, 

 in Tierra del Fuego, the western and southern parts of the archi- 

 pelago are rugged and mountainous, some of the peaks rising from 

 about 3,000 to about 7,000 feet above the sea. (See Fig. 2.) This 

 region represents the southern extension of the Andes, which here 

 turn from their usual north-and-south course to a northwest-and- 

 southeast course, and then to an east-and-west course, finally terminat- 

 ing in the rugged Staten Island, the most easterly member of the 

 archipelago. The northeastern part of the main island of Tierra del 

 Fuego, however, is a more or less flat or rolling country, and partakes 

 of the nature of the pampas of eastern Patagonia, In fact, just as 

 the mountainous districts of Tierra del Fuego are the southerly 

 extension of the Andes, so this part of the main island is geologically 

 the southern extension of the pampas. 



Tierra del Fuego probably owes its condition as a group of islands, 

 instead of as a continuous land area, to a partial submergence of the 

 southern end of South America. The numerous small but high and 

 mountainous islands dropping off precipitously into the sea, following 

 each other in quick succession along certain directions and separated 

 by deep but narrow tidewater channels, strongly suggest what the 



