This package contains the plate tectonic programs backtracker, which you can use to move geologic markers forward or backward in time, grdrotater which rotates entire grids using a finite rotation, hotspotter which generates CVA grids based on seamount locations and a set of absolute plate motion stage poles, originator, which associates seamounts with the most likely hotspot origins, and rotconverter which does various operations involving finite rotations on a sphere. The package is maintained by Paul Wessel.