Daryl Krupa: Geology Question (KRS related)

Daryl:

I'm starting, slowly and carefully, to read the Wolter/Nielsen book, but
I'll admit up front that the reading is being done by sedated eyes since I'm
recovering at home from surgery.

What I've learned, so far, about the geology of the dating method employed
is that a weathering comparison was used to date the inscription by
comparing the KRS (which is greywacke, a meta-sedimentary rock bearing these
micas: biotite, chlorite and muscovite) with three slate (a metamorphic
rock) tombstones from Augusta Maine that were selected from a much larger
number of tombstones because the mica grain size in samples of those three
tombstones was comparable to the grain size of the KRS micas. The authors
only discuss biotite, leading me to believe that the tombstones did not have
the other KRS micas.

The tentative dating for the KRS is "older than 200 years" because all of
the mica minerals on the "man-made surfaces" of the KRS have weathered away
(it's not present in either the inscription or the surfaces bearing the
inscription), while the biotite on the tombstones (average age 194 + or - 5
years) is still present, although it is severly weathered. It is noted that
the tombstones are from a geographical area stated in the text to average 17
inches of rain per year more than falls in Kensington (although tabular data
in the book states that the average is 17 inches of *precipitation*, and
although it is stated that both above and below grade samples should have
been compared, only above-grade samples were collected from the tombstones
because the ground was frozen and covered with a foot of snow.

Leaving aside the issue of differences in average temperatures between
Augusta ME and Kensington, MN, as well as acid rain issues, I'm wondering
whether the comparison made by the authors is geologically sound in the
sense of comparing apples to apples. I don't know enough geology to know
whether the fact that the two rocks are of different types, and the micas on
the two different types of rocks also being different different (the rocks
are reported as having only biotite in common) amounts to comparing apples
to bananas. Any light you could shed on these points would be appreciated.

Steve
--
The above posting is neither a legal opinion nor legal advice,
because we do not have an attorney-client relationship, and
should not be construed as either. This posting does not
represent the opinion of my employer, but is merely my personal
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