ALASKA AND ITS MINERAL RESOURCES 165 



Klondike itself. The placer deposit generally consists of 10 to 

 15 feet of frozen muck and decayed vegetation at the surface, 

 then a gravel bed that rarely pays ; below that a clay selvage, 

 under which is pay dirt, from one to five feet in thickness, rest- 

 ing on the upturned edges of the schist, from which it is separated 

 by a clay selvage. The pay streak or bottom of the old channel 

 is usually very regular and straight, not following the bends of 

 the present stream ; it is said to average 60 cents to the pan, 

 and may yield $1 to $3. Only very exceptionally rich gravel 

 can be worked at all under present conditions. 



Other detrltal deposits. — Besides the placer gravels above de- 

 scribed, there are other detrital deposits that may carry gold, 

 some of which are known to occur in the Yukon district, but 

 have not as yet been extensively worked. In the larger streams 

 accumulations of gravel and sand are made in places of slack- 

 ening current, such as the inner side of curves, or at points where 

 considerable coarse material is brought into the main stream by 

 more rapid tributaries ; such accumulations are called " bars" 

 and often contain much gold. In some cases the entire mass of 

 sand and gravel in a river bed contains enough gold to be worked 

 at a profit by mechanical processes. There must necessarily be 

 a large amount of gold in the bars of the Yukon and its tribu- 

 taries, but whether they are rich enough to be profitably worked 

 under existing conditions has not yet been proved. 



Another common form of detrital deposit is the fine "silts" 

 which often cover wide areas. The most notable instance is what 

 is called the Yukon flats, which extend for a hundred miles or 

 more above and below the great bend of the river at Fort Yukon 

 and a considerable distance up the Porcupine, thus covering an 

 area perhaps 100 by 200 miles in extent. Similar flats, but of 

 more moderate dimensions, occur at various points along the 

 lower course of the river, generally in the concave sides of curves. 

 These silts are being deposited at the present day in the annual 

 floods when the river waters cover such wide areas that their 

 movement becomes as sluggish as those of a lake. There are, 

 however, similar beds of silt of like appearance and constitution 

 at altitudes of several hundred feet above the present stream, 

 which are of widespread occurrence not only in the lower Yukon 

 country but in the plateau region of British Columbia. The 

 latter have been designated white silts by Dr Dawson, who con- 

 siders that they were laid down in fiords connecting with the 

 sea, their material being furnished by the grinding of the re- 



