432 



FORESTRY AND IRRIGATION 



September 



The drill chops down through the soil 

 and loose material, which are forced 

 upward in the casing by passing a 

 stream of water through the tube. 

 The casing follows the bit as it pene- 

 trates downward. On encountering 

 a boulder or other material which re- 

 tards the passage of the casing, the 

 rod and casing are lifted, a charge of 

 dynamite is set off and the obstacle 

 removed. When rock is met with, a 

 circular bit is used in which are in- 

 serted six or eight black diamonds or 

 carbons. The rotary motion of the bit 

 grinds the rock and the core comes up 

 through the bit into the barrel to 

 which the latter is fastened. On the 

 bottom of the barrel just above the bit 

 is what is called the core shell, with a 

 split ring in it, both shell and ring be- 

 ing cone shaped. On pulling out the 

 bit the ring slips down and closes, thus 

 preventing the core from falling out. 



Samples of earth are kept in four 

 ounce bottles, the same dimensions 'as 

 the diamter of core, and all are placed 

 in trays properly labeled for the in- 

 spection of contractors bidding on the 

 work. Each boring shows a complete 

 section of the bottom. With this pro- 

 cess one man made thirty-two moves 

 of machine and put in 1,16.0 feet of 

 boring in six days. The cost of the 

 work varies from 10 cents to $5 per 

 foot, depending on the locality and 

 character of material. 



Notable instances of the unreliabil- 

 ity of surface indications are numer- 

 ous. A few of these may be men- 

 tioned as of particular interest in in- 

 dicating how little dependence may be 

 placed upon surface showings in river 

 canyons. 



In the Shoshone canyon, Wyoming, 

 the river has cut a narrow passage 

 with walls a thousand feet high, 

 through a mountain of granite. Sur- 

 face indications were that the river 

 passed over bed rock and that no trou- 

 ble would be experienced in fixing a 



monster dam immovably upon the sol- 

 idtst sort of a foundation. But the 

 drill quickly dissipated this hope. It 

 took all winter to find bed rock, and 

 ir was only after a number of moves 

 up and down stream that a suitable 

 location was found. Here bed rock 

 was found at 65 feet, after passing 

 through boulders 30 feet in diameter 

 en top of beds of gravel. At the point 

 first selected for a site, bed rock was 

 found at a depth of 88 feet, and bor- 

 ings were continued to a much greater 

 depth to make sure that a solid foun- 

 dation had at last been reached. At 

 the Pathfinder dam site in Wyoming, 

 where the surface conditions were 

 practically identical, bed rock was 

 found at a depth of 5 feet. 



On the Colorado River between 

 Yuma and the mouth of the Grand 

 Canyon, the government expended 

 $40,000 on drilling and then failed to 

 find a permanent base for a darn. At 

 the Laguna dam site, near Yuma, the 

 river passes between granite w r alls, and 

 in the channel rocky ledges extrude in 

 several places. The drill showed that 

 these ledges were not connected at the 

 bottom ; that between them were great 

 wide pockets of sand 168 feet in depth. 

 This condition necessitated complete 

 change of plans for a structure. 



The engineers have completed pre- 

 liminary borings in the Klamath coun- 

 try, southern Oregon, finding good 

 formation near the surface for a dam 

 site. Borings were made there for a 

 tunnel no feet below the surface and 

 1,500 feet long, which is to take water 

 around and outside the town. 



At the Malheur dam site bed rock 

 was found at 28 feet in a first-class lo- 

 cation. At Minidoka, Idaho, the river 

 cuts through a lava ridge and perma- 

 nent foundation was found at 20 feet. 

 Work is now being carried on by dril- 

 ling parties in North Dakota, Okla- 

 homa, California, Utah, New Mexico, 

 Colorado, Montana, and Oregon. 



