98 B. K. EMERSON — TETRAHEDRAL EARTH: INTERCONTINENTAL SEAS 



make the comparison difficult. In the interior of Alaska, however, con- 

 ditions of a wholly different kind appear. A great gneiss chain extends 

 nearly from west to east about in the direction of the Xanana river, north 

 and south of the sixty-fourth parallel and in the chord of the arc of the 

 Yukon. It turns then east-southeast and southeast, and forms the water- 

 shed between the Pelly and the Lewes, follows the course of the Findlay, 

 and is considered as the continuation, perhaps locally interrupted, of the 

 Caribou region and the Golden ranges in British Columbia. Associated 

 with this chain, especially along its northern border, are ancient sedi- 

 ments altered by pressure, which are the source of the gold of Alaska. 



This is followed, far to the northeast and east, by the zone of great fault- 

 blocks, which is here called the Rocky mountains. 



Its outer border extends from the mouth of the Mackenzie down to 

 Wyoming. In other words, there is in British Columbia an extensive 

 one-sided chain, folded and overthrust toward the east, whose western part 

 is formed by the Golden ranges (Selkirk, etcetera). This chain, which in 

 British Columbia strikes north-northwest, bends around so that in mid- 

 dle Alaska it strikes east-west and is there folded toward the north. On 

 the west the ancient granite and gneiss do not reach the lower Yukon, 

 but the gold-bearing rocks outcrop in low hills in about 65 degrees north 

 on the lower course of the river. 



This range is therefore wholly foreign to the Werchojan range. On 

 the other hand, there appears on the west coast of British Columbia a 

 very thick belt of granite, often accompanied on its west side by vol- 

 canic occurrences. It forms the Coast ranges which pass in a course to 

 the north of Mount Saint Elias, and in all probability meets in union 

 (in Schaarung) with the curve of the Aleutians. 



The curve of the Aleutians is the last toward the east which shows the 

 typical form of the inland curve. The Commanders islands differ some- 

 what in their composition from the Aleutian, so that the contact with 

 Ivamschatka is doubtful. The Tertiary beds, partially marine, which are 

 extensively developed on the lower Yukon and in the Aleutians, prob- 

 ably also form the Karagin island. They are also met in the gulf of 

 Penschin and perhaps underlie the tundra which separates Ivamschatka 

 from the Werchojan curve. 



All the above named mountain chains from the Kanin peninsula on 

 to Bering sea, stand in contrast to the Eur-Asiatic folds, as wholly foreign 

 to them or at least as not fitting into the general plan which controls 

 them. All are folded toward the west, south, or east and open toward 

 the pole. The}'' have no equivalents in North America except, perhaps, 

 the Coast ranges. Horizontal Paleozoic tablelands extend over the Arctic 

 archipelago of North America. 



