Eskola would no doubt be pleased to read
Howard Day's reminder that the facies
classification of rocks is natural
rather than artificial. Natural
classifications are based upon
properties rather than attributes.
The 'quality' of metamorphism is the sum
of those natural properties attributed
to this phenomenon the rock displays:
texture, fabric, mineral assemblage, &
other properties that can be observed or
measured objectively. An artificial
class is based upon attributes we
assign: petrogeneses determined
subjectively, divisions selected
arbitrarily, measures calculated from
theory.
Natural classes are important because
their correlation tells us about nature
rather than about ourselves. Though
Becke's two-fold and Grubenmann's
three-fold divisions of metamorphic
grade might sound artificial, they were
carefully defined, natural
classifications, as Eskola's is.
I'm emphasizing the obvious here only
because much nomenclature proposed by
the SCMR appears to me unnecessarily
artificial.
Bruce Bathurst
|