98 GRAVEL AND PLACER MINING IN ALASKA. [bull. 263. 
being wet. The obscurity of the air in the workings by steam, espe- 
cially in the early part of the day shift, is frequently a source of dan- 
ger, as the roof can not be watched so closely as it could were the air 
clear, and consequently slabs of the roof that are ready to fall can not 
be easily seen, so that the liability that men will be crushed is greater. 
I should especially recommend the method of hot-water thawing 
to the consideration of the miners of Cleary and Pedro creeks, while 
on Fairbanks Creek, as hitherto developed, the method of thawing 
with steam points seems more applicable. 
In the Fairbanks district shafts sunk for work in the summer time 
are in nearly all cases timbered, either wholly or partially. In very, 
deep shafts, as, for example, on the left bank of Cleary Creek near 
the junction with Chatham, where 40 feet or more of solid muck is 
encountered, timbering does not appear to be always necessary through- 
out the whole of the shaft. The muck forms a wall which resembles 
in its consistency a wall of solid ice, and in working throughout a 
season of four months, with the shaft in constant use, there will be 
little caving of the walls. All shafts that extend 20 feet or less, how- 
ever, especially where gravel composes half or more of the section — 
shafts intended for working out a block of ground, conducting steam] 
connections, pump connections, and connections for hoisting — should 
be securely timbered. 
In view of the local conditions, the following method of timbering 
appears the most satisfactor}^. After the hole is sunk to the required 
depth by thawing, a square set with 6-foot centers — or should the shaft 
be 4 by 6 feet, of this dimension — is put in at the bottom. Three- 
inch pole lagging, with cross sets of 0-inch timbers inside at 6-foot 
intervals, is carried up to the collar. Inside the sets 6- or 12-foot 
poles, 3-inch, are nailed in the four corners to the cross sets. Moss is 
laid up outside the pole lagging, as dry as possible, and packed against 
the gravel or muck walls. In cases where it is impossible to sink with- 
out timbering as the shaft is sunk the timbering is carried down, and 
the lagging is driven as each set progresses, the square set being put 
in at the bottom on the completion of the shaft. Shafts timbered ia 
this manner have been found to stand for periods of from one to two 
years, as long as the work in the Fairbanks district has been in prog- 
ress, and there is no reason why they should not stand much longer.! 
Timbering of this sort can be done for the most part with the ordinary 
cord wood delivered for fuel, and this is much the cheapest method 
available. 
The cribbing method is sometimes adopted, accompanied by the same 
packing, with moss outside the cribbing. It is, however, more expen- 
sive, and in a shaft of considerable depth is much more likely to get 
out of plumb in this frost-ridden country. 
