RECITALS:

   1
                                                                    Exhibit 4.10
                                                                    ------------

                             SUPPLEMENTAL INDENTURE


         Reference is made to that certain Indenture, dated as of February 1,
1999, by and among Oglebay Norton Company (formerly known as Oglebay Norton
Holding Company), a Delaware corporation ("Oglebay"), the guarantors party
thereto and NORWEST BANK MINNESOTA, NATIONAL ASSOCIATION, as Trustee (the
"Indenture"). Capitalized terms used without definition herein have the meanings
given to them in the Indenture.

                                    RECITALS:

         X. Xxxxxxx recently formed three wholly owned subsidiaries: (i) ONCO
Investment Company, a Delaware corporation ("Investment Company"), (ii) Oglebay
Norton Marine Services Company, L.L.C., a Delaware limited liability company
("Oglebay, L.L.C."), and (iii) Global Xxxxx Xxxxx River, Inc. ("Xxxxx River");

         B. The Indenture requires Investment Company, Oglebay, L.L.C. and Xxxxx
River to become Guarantors under the Indenture, unless they are designated as
unrestricted subsidiaries;

         NOW, THEREFORE, in consideration of the above premises, Investment
Company, Oglebay, L.L.C. and Xxxxx River agree, for the benefit of the Holders,
as follows:

         Effective as of the date below, Investment Company, Oglebay, L.L.C. and
Xxxxx River hereby expressly and fully and unconditionally agree to become
Guarantors under the Financing Documents.

         The laws of the State of New York shall govern this Supplemental
Indenture without giving effect to any conflicts of law principles thereof.





   2


         IN WITNESS WHEREOF, the undersigned has caused this Supplemental
Indenture to be duly executed, all as of April 12, 1999.

                                     ONCO INVESTMENT COMPANY

                                     By:      /s/ Xxxxxxx X. Xxxx
                                        ---------------------------------------
                                           Name:  Xxxxxxx X. Xxxx
                                           Title:    Vice President

                                     OGLEBAY NORTON MARINE SERVICES, L.L.C.

                                     By:  ON MARINE SERVICES COMPANY, as sole
                                             member

                                              By:  /s/ Xxxxxxx X. Xxxx
                                                 ------------------------------
                                                   Name:  Xxxxxxx X. Xxxx
                                                   Title:    Vice President

                                     GLOBAL XXXXX XXXXX RIVER, INC.

                                     By:    /s/ Xxxxxxx X. Xxxx
                                        ---------------------------------------
                                           Name:  Xxxxxxx X. Xxxx
                                           Title:    Vice President

                                     NORWEST BANK MINNESOTA,
                                     NATIONAL ASSOCIATION

                                     By:   /s/ Xxxxxx X. Xxxxxxxxx
                                        ---------------------------------------
                                           Name:  Xxxxxx X. Xxxxxxxxx
                                           Title:    Assistant Vice President