34 THE UNITED STATES GEOLOGICAL SURVEY. [bull. 227. 
has the form of an arc, concave toward the open ocean, but the con- 
tinuity of this great curve is interrupted by many inlets. The western 
boundary of Alaska has the appearance of incompleteness. One looks 
involuntarily for its continuation and finds it in Siberia. It is very 
probable that at one or more times in its history Alaska has been con- 
nected by land with the latter country, and even at the present time 
the waters of Bering Strait have a depth of hardly 200 feet. This 
western boundary is indented by Kotzebue and Norton sounds, which 
separate the land mass into three bulky portions, the middle one of 
which, Seward Peninsula, approaches nearest to Siberia. The arc of 
the southern coast is reversed in the Aleutian Islands, and the concave 
side is occupied by Bering- Sea. The distance from the end of the Pan- 
handle to the outermost of the Aleutian Islands is about equal to that 
from the Atlantic to the Pacific, and between the same point and the 
Arctic Ocean is included a stretch of country equal to that from Florida 
to Canada. The northern coast is regular, and from it the sea floor 
slopes gently beneath the waters of the Arctic Ocean. 
The surface of Alaska exhibits a wealth of topographic features of 
contrasting variety — mountains, plateaus, and lowlands — developed on 
a truly grand scale. 
In a broad way, the larger features of topography correspond with 
those of the Western States. There is a Pacific Mountain system, a 
plateau region, a Rocky Mountain system, and a plains region. These 
four divisions are well marked and show the close geographic relation 
of this area to the southern part of the continent. Through the States 
and British Columbia the mountain trends are north-south and 
northwest-southeast, but after they enter Alaska they swerve to the 
west, and finally to the southwest, and thus determine the configuration 
of the southern coasts and the valley of the Yukon River. The irregu- 
lar appearance of the western coast is due to the western trend of the 
main lines of structure, which find their continuation on the other side 
of Bering Sea. 
THE MOUNTAINS. 
The Pacific Mountain system has been divided into four ranges — the 
Coast, the St. Elias, the Aleutian, and the Alaskan. These subdivi- 
sions of the system ma} 7 be recognized in the model exhibited by the 
Geological Survey at the Louisiana Purchase Exposition in 1904. 
The greater part of the Coast Range lies back of the Panhandle of 
Alaska, in British Columbia. It attains a width of 100 miles and a 
height of 7,000 to 8,000 feet, but shows no well-defined crest line. 
Closely associated with these mountains in the islands of the Pan- 
handle are the beginnings of the St. Elias Range, which, farther west, 
includes that magnificent group, the Fairweather Mountains, and still 
farther westward attains its fullest expression in the lofty summits of 
