26 NEW YORK STATE MUSEUM 



could be relied upon became involved at once with an interpretation 

 of local glacial phenomena, especially an interpretation of the char- 

 acter of the local drift. In order to see the limited application of 

 this method one needs only to point out that the majority of drift 

 deposits in this region are stony or even bouldery, forming thick 

 coverings in the valleys, and to call attention to the experience at 

 two or three points. For example, at ]\Ioodna creek, the prelimi- 

 nary wash borings were obstructed and bed rock reported at 5 to 

 15 feet below the surface where afterward, by other means, it was 

 proven to lie more than 300 feet down. Or again, in the pre- 

 liminary wash borings in the Hudson, the rigs were stopped and 

 rock bottom provisionally reported at from 25 to 200 feet below 

 sea level, but later explorations have proven at the same point that 

 rock bottom is more than 700 feet down. 



Therefore, to the " wash rig '' was added the "chop drill" and 

 the '' oil-well rig " and to these, or to modifications of them,^ the 

 success in reaching bed rock has been due. 



From independent field studies of a more strictly geologic nature 

 it became clear that many of the valleys, where pressure tunnels 

 were proposed, are of comparatively complex geologic structure and 

 exhibit considerable variety of rock quality and condition. This 

 then introduced and necessitated still more elaborate lines of ex- 

 ploration. It w^as not enough to know the profile of rock floor 

 alone, it became of equal importance to penetrate the rock and obtain 

 samples of it. So the shot drill - and the diamond drill ^ were 

 employed and the drill cores preserved for identification and 

 reference. 



1 The essential features of the machines in most instances are, a high 

 tower or support, a heavy chisel-shaped plunger that can be raised by 

 a rope and dropped repeatedly in the hole, destroying or displacing 

 obstructions, and which can be followed by a casing driven down as 

 progress is made — a combination of washing, chopping and driving. 



2 The shot drill, or calyx drill, is essentially a machine devised to rotate 

 a steel tube which is so adjusted and manipulated that a supply of small 

 chilled shot can be kept continually under the lower end as it bores into 

 the rock. The cutting is done by the shot immediately under the edge 

 of the tube. A core remains in the tube and may be recovered. Its best 

 position is vertical. 



3 The diamond drill consists essentially of a bit or crown set with black 

 diamonds (bort) in such manner that when the bit is attached to a rotating 

 tube a circular groove is cut into the rock. By proper attachment to 

 jointed tubes and driving gear a hole may thus be bored at any angle and 

 to great depth and a core recovered. 



