The text of this manuscript was converted to postscript from
a WordPerfect file but should be readable. The figures are included
in separate files. Figures 1 and 2 are have not yet been
scanned in; if you really need them, or if you have any other
questions or comments, please contact me.
Nick Street
nick-street@uiowa.edu
manuscript
figure 3
figure 4
figure 5
figure 6