<PAGE>
 
      6. This Agreement shall not be modified, amended, altered or supplemented
except by a written agreement executed by all of the parties hereto. In the
event of a termination of the Merger, Purchase and Sale Agreement pursuant to
the terms of Article VII thereof, or in the event that the Merger is otherwise
not consummated on or before December 1, 1993, this Agreement shall also
terminate.

      7. This Agreement may be executed in two or more counterparts, each of
which shall be deemed to be an original, but all of which together shall
constitute one and the same document. This Agreement constitutes the entire
agreement among the Parties with respect to the subject matter hereof.

      IN WITNESS WHEREOF, the parties hereto have caused this Continuity of
Interest Agreement to be duly executed this 18th day of November, 1993 to be
effective for all purposes as of November 9, 1993.


                                            -----------------------------------
                                            Peter M. Holt


                                            -----------------------------------
                                            Benjamin D. Holt, Jr.



                                            PETER HOLT H-R TRUST


                                            By: _______________________________
                                                Peter M. Holt
                                                Trustee


                                            S STOCK GST TRUST FOR
                                            PETER M. HOLT


                                            By: _______________________________
                                                Peter M. Holt
                                                Trustee


                                            By: _______________________________
                                                Benjamin D. Holt, Jr.
                                                Trustee

                                      -3-