ERRATA

1. Page 43, line 8:
   Please add ``-G mu (1-lambda)'' to the RHS of the equation involving the pressures.

2. Page 46, equation (25):
   Please modify the LHS to read: `` Psi<sub>j</sub>(x, sigma, t)'';
   insert a minus sign next to the ``='' sign;
   change ``cos'' to``sin''.

3. Page 47, second line after equation (29):
   Please change ``(3.6)'' to ``(36)''.

4. Page 47, equation (30):
   Please change ``u'' to ``u'' on the LHS;
   change ``sigma'' to ``f'' in two places on the RHS;
   change ``z'' to ``x'' on the RHS.