Modified code so that instead of computing error by bootstrapping the
residuals, I simply make sure the residuals look alright and calculate
their standard deviation.  The code includes an option to log transform
the data before this calculation is done.  Many of the plates and
bedrocks are failing some of the tests that ensure the residuals can be
used to calculate standard deviation.  For example, some residuals are
not homoscedastic, and some are not normally distributed.  I'm not sure
what to do about this.