The example of fissile metamorphic slate illustrated here came
from along Curve #149 on Track #2 of the Sierra grade where it
had fallen from the excavated face of Cape Horn. Originally
formed under the sea over 200,000,000 years ago during the
Mesozoic era as sedimentary rock, it was eventually lifted up
and slowly changed into its present form over millions of years
by heat and pressure exerted on it from below by pools of molten
magma rising through the earth's crust. When this underlying
magma finally cooled it became one of the some 200 granite
plutons which now make up the sierra nevada batholith. The
original Cape Horn grade, as located by resident engineer Lewis
M. Clement, was a narrow ledge just barely wide enough to
support the single track it carried. Constructed in 1865-66 by
the CPRR's industrious crews of Chinese workers, it was
literally "carved" out of the rock using hand drills and black
powder, and by filling in a number of deep gullies between the
outcrops. (The SP finally widened the grad