Travel Reference
In-Depth Information
It takes two to drill—one to do the actual drilling, the other to pump
the water. Water? Somehow the water hadn't come up when I received my
first sales pitch from Dr. Verosub, who, like any good used-car salesman,
also declined to spend any time in the field actually drilling the tocks after
our first trial run. The drilling requires that copious quantities of fresh
water be pumped constantly through the drill while it is in contact with
the rock. Spinning at propeller-like speed, it also emits the scteeching
characteristic of chain saws (but elevated in pitch because of the diamond-
on-rock contact). I quickly found that coring rocks for paleomagnetic sam-
pling was anything but a rest cure. The drill had to be muscled into place,
and the coring of the rock, accompanied by the constant stream of water
being pumped into the hole, enveloped the operation in a fine stream of
muddy haze. The driller was soon coated with wet mud. Three cores were
taken at each locality, and we drilled a new locality in each meter or in
several meters of layered rock. Because our first sampling creek, Chico
Creek, was over 500 meters thick, we were soon locked into a long-term
endeavor. On a good day we could obtain about 100 cores, but we often
got less.
Yet the drilling turned out to be the
easiest
part of the operation, for
once the holes were bored into the rock, the cores had to be extracted and
their orientation noted. Orientation was found by inserting a brass sleeve
around the core (which, if we were fortunate, was still in the rock, attached
at its base, and not broken off and jammed inside the drill). The sleeve had
a platform on top, which was machined so that it held a geologist's compass.
When leveled, the compass showed the orientation of the core, and a second
measurement yielded the plunge, or the angle of its entrance into the rock.
Given these two observations, coupled with a measurement of the orienta-
tion of the sedimentary beds themselves (which sometimes were in their
original, flat-lying orientation but more often were tilted at some angle, a
complication that had to be accounted for), a computer could calculate the
original orientation of the core.
All this took time—time to select a site, time to drill it, and much time
to take the accurate measurements necessary to arrive at core orientation.
