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                                                                     EXHIBIT 4.1

                          SIXTH SUPPLEMENTAL INDENTURE

      SIXTH SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
January 20, 2005, by and among the entities listed on Schedule 1 attached hereto
(the "Guaranteeing Subsidiaries"), each being a subsidiary of Peabody Energy
Corporation (or its permitted successor), a Delaware corporation (the
"Company"), the Company, the other Subsidiary Guarantors (as defined in the
Indenture referred to herein) and US Bank National Association, as Trustee under
the Indenture referred to below (the "Trustee").

                                   WITNESSETH

      WHEREAS, the Company has heretofore executed and delivered to the Trustee
an Indenture (the "Indenture"), dated as of March 21, 2003 providing for the
issuance of an unlimited amount of 6-7/8% Notes due 2013 (the "Notes"), as
supplemented by a First Supplemental Indenture, dated as of May 7, 2003; Second
Supplemental Indenture, dated as of September 30, 2003;Third Supplemental
Indenture, dated as of February 24, 2004; and Fourth Supplemental Indenture,
dated April 22, 2004; and Fifth Supplemental Indenture, dated October 18, 2004;

      WHEREAS, the Indenture provides that under certain circumstances the
Guaranteeing Subsidiaries shall execute and deliver to the Trustee a
supplemental indenture pursuant to which the Guaranteeing Subsidiaries shall
unconditionally guarantee all of the Company's Obligations under the Notes on
the terms and conditions set forth herein (the "Subsidiary Guarantee"); and

      WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

      NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Guaranteeing Subsidiaries and the Trustee mutually covenant and agree for the
equal and ratable benefit of the Holders of the Notes as follows:

      1.    CAPITALIZED TERMS. Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

      2.    AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiaries hereby agree
as follows:

            (a)   Along with all Subsidiary Guarantors named in the Indenture,
                  to jointly and severally Guarantee to each Holder of a Note
                  authenticated and delivered by the Trustee and to the Trustee
                  and its successors and assigns, irrespective of the validity
                  and

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                  enforceability of the Indenture, the Notes or the obligations
                  of the Company hereunder or thereunder, that:

                  (i)   the principal of and interest on the Notes will be
                        promptly paid in full when due, whether at maturity, by
                        acceleration, redemption or otherwise, and interest on
                        the overdue principal of and interest on the Notes, if
                        any, if lawful, and all other obligations of the Company
                        to the Holders or the Trustee hereunder or thereunder
                        will be promptly paid in full or performed, all in
                        accordance with the terms hereof and thereof; and

                  (ii)  in case of any extension of time of payment or renewal
                        of any Notes or any of such other obligations, that same
                        will be promptly paid in full when due or performed in
                        accordance with the terms of the extension or renewal,
                        whether at stated maturity, by acceleration or
                        otherwise.

                  Failing payment when due of any amount so guaranteed or any
                  performance so guaranteed for whatever reason, the Subsidiary
                  Guarantors shall be jointly and severally obligated to pay the
                  same immediately. Each Subsidiary Guarantor agrees that this
                  is a guarantee of payment and not a guarantee of collection.

            (b)   The obligations hereunder shall be joint and several and
                  unconditional, irrespective of the validity or enforceability
                  of the Notes or the obligations of the Company under the
                  Indenture, the absence of any action to enforce the same, any
                  waiver or consent by any Holder of the Notes with respect to
                  any provisions hereof or thereof, the recovery of any judgment
                  against the Company, any action to enforce the same or any
                  other circumstance which might otherwise constitute a legal or
                  equitable discharge or defense of a Subsidiary Guarantor.

            (c)   The following is hereby waived: diligence, presentment, demand
                  of payment, filing of claims with a court in the event of
                  insolvency or bankruptcy of the Company, any right to require
                  a proceeding first against the Company, protest, notice and
                  all demands whatsoever.

            (d)   This Subsidiary Guarantee shall not be discharged except by
                  complete performance of the obligations contained in the Notes
                  and the Indenture.

            (e)   If any Holder or the Trustee is required by any court or
                  otherwise to return to the Company, the Subsidiary Guarantors,
                  or any custodian, Trustee, liquidator or other similar
                  official acting in

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                  relation to either the Company or the Subsidiary Guarantors,
                  any amount paid by either to the Trustee or such Holder, this
                  Subsidiary Guarantee, to the extent theretofore discharged,
                  shall be reinstated in full force and effect.

            (f)   The Guaranteeing Subsidiaries shall not be entitled to any
                  right of subrogation in relation to the Holders in respect of
                  any obligations guaranteed hereby until payment in full of all
                  obligations guaranteed hereby.

            (g)   As between the Subsidiary Guarantors, on the one hand, and the
                  Holders and the Trustee, on the other hand, (x) the maturity
                  of the obligations guaranteed hereby may be accelerated as
                  provided in Article 6 of the Indenture for the purposes of
                  this Subsidiary Guarantee, notwithstanding any stay,
                  injunction or other prohibition preventing such acceleration
                  in respect of the obligations guaranteed hereby, and (y) in
                  the event of any declaration of acceleration of such
                  obligations as provided in Article 6 of the Indenture, such
                  obligations (whether or not due and payable) shall forthwith
                  become due and payable by the Subsidiary Guarantors for the
                  purpose of this Subsidiary Guarantee.

            (h)   The Subsidiary Guarantors shall have the right to seek
                  contribution from any non-paying Subsidiary Guarantor so long
                  as the exercise of such right does not impair the rights of
                  the Holders under the Subsidiary Guarantee.

            (i)   Pursuant to Section 10.04 of the Indenture, after giving
                  effect to any maximum amount and any other contingent and
                  fixed liabilities that are relevant under any applicable
                  Bankruptcy or fraudulent conveyance laws, and after giving
                  effect to any collections from, rights to receive contribution
                  from or payments made by or on behalf of any other Subsidiary
                  Guarantor in respect of the obligations of such other
                  Subsidiary Guarantor under Article 10 of the Indenture shall
                  result in the obligations of such Subsidiary Guarantor under
                  Subsidiary Guarantee not constituting a fraudulent transfer or
                  conveyance.

      3.    EXECUTION AND DELIVERY. Each of the Guaranteeing Subsidiaries agrees
that the Subsidiary Guarantees shall remain in full force and effect
notwithstanding any failure to endorse on each Note a notation of such
Subsidiary Guarantee.

      4.    GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

            (a)   The Guaranteeing Subsidiaries may not consolidate with or
                  merge with or into (whether or not such Senior Subordinated
                  Note

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            Guarantor is the surviving Person) another corporation, Person or
            entity whether or not affiliated with such Subsidiary Guarantor
            unless:

                  (i)   subject to Section 10.04 of the Indenture, the Person
                        formed by or surviving any such consolidation or merger
                        (if other than a Subsidiary Guarantor or the Company)
                        unconditionally assumes all the obligations of such
                        Subsidiary Guarantor, pursuant to a supplemental
                        Indenture in form and substance reasonably satisfactory
                        to the Trustee, under the Notes, the Indenture and the
                        Subsidiary Guarantee on the terms set forth herein or
                        therein; and

                  (ii)  immediately after giving effect to such transaction, no
                        Default or Event of Default exists.

            (b)   In case of any such consolidation, merger, sale or conveyance
                  and upon the assumption by the successor corporation, by
                  supplemental Indenture, executed and delivered to the Trustee
                  and satisfactory in form to the Trustee, of the Subsidiary
                  Guarantee endorsed upon the Notes and the due and punctual
                  performance of all of the covenants and conditions of the
                  Indenture to be performed by the Subsidiary Guarantor, such
                  successor corporation shall succeed to and be substituted for
                  the Subsidiary Guarantor with the same effect as if it had
                  been named herein as a Subsidiary Guarantor. Such successor
                  corporation thereupon may cause to be signed any or all of the
                  Subsidiary Guarantees to be endorsed upon all of the Notes
                  issuable hereunder which theretofore shall not have been
                  signed by the Company and delivered to the Trustee. All the
                  Subsidiary Guarantees so issued shall in all respects have the
                  same legal rank and benefit under the Indenture as the
                  Subsidiary Guarantees theretofore and thereafter issued in
                  accordance with the terms of the Indenture as though all of
                  such Subsidiary Guarantees had been issued at the date of the
                  execution hereof.

            (c)   Except as set forth in Articles 4 and 5 of the Indenture, and
                  notwithstanding clauses (a) and (b) above, nothing contained
                  in the Indenture or in any of the Notes shall prevent any
                  consolidation or merger of a Subsidiary Guarantor with or into
                  the Company or another Subsidiary Guarantor, or shall prevent
                  any sale or conveyance of the property of a Subsidiary
                  Guarantor as an entirety or substantially as an entirety to
                  the Company or another Subsidiary Guarantor.

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<PAGE>

      5.    RELEASES.

            (a)   In the event of a sale or other disposition of all of the
                  assets of any Subsidiary Guarantor, by way of merger,
                  consolidation or otherwise, or a sale or other disposition of
                  all to the capital stock of any Subsidiary Guarantor, then
                  such Subsidiary Guarantor (in the event of a sale or other
                  disposition, by way of merger, consolidation or otherwise, of
                  all of the capital stock of such Subsidiary Guarantor) or the
                  corporation acquiring the property (in the event of a sale or
                  other disposition of all or substantially all of the assets of
                  such Subsidiary Guarantor) will be released and relieved of
                  any obligations under its Subsidiary Guarantee; provided that
                  the Net Proceeds of such sale or other disposition are applied
                  in accordance with the applicable provisions of the Indenture,
                  including without limitation Section 4.10 of the Indenture.
                  Upon delivery by the Company to the Trustee of an Officer's
                  Certificate and an Opinion of Counsel to the effect that such
                  sale or other disposition was made by the Company in
                  accordance with the provisions of the Indenture, including
                  without limitation Section 4.10 of the Indenture, the Trustee
                  shall execute any documents reasonably required in order to
                  evidence the release of any Subsidiary Guarantor from its
                  obligations under its Subsidiary Guarantee.

            (b)   Any Subsidiary Guarantor not released from its obligations
                  under its Subsidiary Guarantee shall remain liable for the
                  full amount of principal of and interest on the Notes and for
                  the other obligations of any Subsidiary Guarantor under the
                  Indenture as provided in Article 10 of the Indenture.

      6.    NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, stockholder or agent of the Guaranteeing
Subsidiaries, as such, shall have any liability for any obligations of the
Company or any of the Guaranteeing Subsidiaries under the Notes, any Subsidiary
Guarantees, the Indenture or this Supplemental Indenture or for any claim based
on, in respect of, or by reason of, such obligations or their creation. Each
Holder of the Notes by accepting a Note waives and releases all such liability.
The waiver and release are part of the consideration for issuance of the Notes.
Such waiver may not be effective to waive liabilities under the federal
securities laws and it is the view of the Commission that such a waiver is
against public policy.

      7.    NEW YORK LAW TO GOVERN. THE LAW OF THE STATE OF NEW YORK SHALL
GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE.

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<PAGE>

      8.    COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

      9.    EFFECT OF HEADINGS. The Section headings herein are for convenience
only and shall not affect the construction hereof.

      10.   THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiaries and the Company.

      IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be executed by their respective officers thereunto duly authorized,
as of the date first written above.

PEABODY ENERGY CORPORATION                  US BANK NATIONAL ASSOCIATION
("COMPANY")                                 ("TRUSTEE")

By: /s/ Walter L. Hawkins, Jr.                    By: /s/Philip G. Kane, Jr.
    ---------------------------                       --------------------------
Name: Walter L. Hawkins, Jr.                      Name: Philip G. Kane, Jr.
Title: Vice President and Treasurer               Title: Vice President

EXISTING SUBSIDIARY GUARANTORS:

                            AFFINITY MINING COMPANY
                            APPALACHIA MINE SERVICES, LLC
                            ARCLAR COMPANY, LLC
                            ARID OPERATIONS INC.
                            BEAVER DAM COAL COMPANY
                            BIG RIDGE, INC.
                            BIG SKY COAL COMPANY
                            BLACK BEAUTY COAL COMPANY
                            BLACK BEAUTY EQUIPMENT COMPANY
                            BLACK BEAUTY HOLDING COMPANY, LLC
                            BLACK BEAUTY MINING, INC.
                            BLACK BEAUTY RESOURCES, INC.
                            BLACK BEAUTY UNDERGROUND, INC.
                            BLACK HILLS MINING COMPANY, LLC
                            BLACK STALLION COAL COMPANY, LLC
                            BLACK WALNUT COAL COMPANY
                            BLUEGRASS COAL COMPANY
                            BTU EMPIRE CORPORATION
                            BTU VENEZUELA, LLC
                            CABALLO COAL COMPANY
                            CHARLES COAL COMPANY
                            CLEATON COAL COMPANY
                            COAL PROPERTIES CORP.
                            COALSALES, LLC

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<PAGE>

                            COALSALES II, LLC f/k/a PEABODY COALSALES COMPANY
                            COALTRADE INTERNATIONAL, LLC
                                     f/k/a PEABODY COALTRADE INTERNATIONAL, LLC
                            COALTRADE, LLC f/k/a PEABODY COALTRADE, INC.
                            COAL RESERVES HOLDING LIMITED LIABILITY
                            COMPANY NO. 1
                            COAL RESERVES HOLDING LIMITED LIABILITY
                            COMPANY NO. 2
                            COLONY BAY COAL COMPANY
                            COLORADO YAMPA COAL COMPANY
                            COOK MOUNTAIN COAL COMPANY
                            COTTONWOOD LAND COMPANY
                            CYPRUS CREEK LAND COMPANY
                            CYPRUS CREEK LAND RESOURCES, LLC
                            EACC CAMPS, INC.
                            EAGLE COAL COMPANY
                            EASTERN ASSOCIATED COAL CORP.
                            EASTERN ROYALTY CORP.
                            EMPIRE MARINE, LLC
                            FALCON COAL COMPANY
                            GALLO FINANCE COMPANY
                            GIBCO MOTOR EXPRESS, LLC
                            GOLD FIELDS CHILE, S.A.
                            GOLD FIELDS MINING, LLC f/k/a GOLD FIELDS MINING
                                              CORPORATION
                            GOLD FIELDS OPERATING CO. - ORTIZ
                            GRAND EAGLE MINING, INC.
                            HAYDEN GULCH TERMINAL, INC.
                            HIGHLAND MINING COMPANY
                            HIGHWALL MINING SERVICES COMPANY
                            HILLSIDE MINING COMPANY
                            INDEPENDENCE MATERIAL HANDLING
                                 COMPANY
                            INDIAN HILL COMPANY
                            INTERIOR HOLDINGS CORP.
                            JAMES RIVER COAL TERMINAL COMPANY
                            JARRELL'S BRANCH COAL COMPANY
                            JUNIPER COAL COMPANY
                            KANAWHA RIVER VENTURES I, LLC
                            KAYENTA MOBILE HOME PARK, INC.
                            LOGAN FORK COAL COMPANY
                            MARTINKA COAL COMPANY
                            MIDCO SUPPLY AND EQUIPMENT
                                 CORPORATION
                            MIDWEST COAL ACQUISITION CORP.
                            MOUNTAIN VIEW COAL COMPANY
                            MUSTANG ENERGY COMPANY, L.L.C.
                            NORTH PAGE COAL CORP.
                            OHIO COUNTY COAL COMPANY
                            PATRIOT COAL COMPANY, L.P.
                            PDC PARTNERSHIP HOLDINGS, INC.
                            PEABODY AMERICA, INC.
                            PEABODY ARCHVEYOR, L.L.C.
                            PEABODY COAL COMPANY
                            PEABODY DEVELOPMENT COMPANY,LLC
                            PEABODY DEVELOPMENT LAND HOLDINGS, LLC

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                            PEABODY ENERGY GENERATION HOLDING COMPANY
                            PEABODY ENERGY INVESTMENTS, INC.
                            PEABODY ENERGY SOLUTIONS, INC.
                            PEABODY HOLDING COMPANY, INC.
                            PEABODY INVESTMENTS CORP.
                                     f/k/a BTU WORLDWIDE, INC.
                            PEABODY NATURAL GAS, LLC
                            PEABODY NATURAL RESOURCES COMPANY
                            PEABODY POWERTREE INVESTMENTS, LLC
                            PEABODY RECREATIONAL LANDS, L.L.C.
                            PEABODY SOUTHWESTERN COAL COMPANY
                            PEABODY TERMINALS, INC.
                            PEABODY VENEZUELA COAL CORP.
                            PEABODY-WATERSIDE DEVELOPMENT, L.L.C.
                            PEABODY WESTERN COAL COMPANY
                            PEC EQUIPMENT COMPANY, LLC
                            PINE RIDGE COAL COMPANY
                            POINT PLEASANT DOCK COMPANY, LLC
                            POND CREEK LAND RESOURCES, LLC
                            POND RIVER LAND COMPANY
                            PORCUPINE PRODUCTION, LLC
                            PORCUPINE TRANSPORTATION, LLC
                            POWDER RIVER COAL COMPANY
                            PRAIRIE STATE GENERATING COMPANY, LLC
                            RIO ESCONDIDO COAL CORP.
                            RIVERS EDGE MINING, INC.
                            RIVERVIEW TERMINAL COMPANY
                            SENECA COAL COMPANY
                            SENTRY MINING COMPANY
                            SHOSHONE COAL CORPORATION
                            SNOWBERRY LAND COMPANY
                            STAR LAKE ENERGY COMPANY, L.L.C.
                            STERLING SMOKELESS COAL COMPANY
                            SUGAR CAMP PROPERTIES
                            THOROUGHBRED, L.L.C.
                            THOROUGHBRED GENERATING COMPANY, LLC
                            THOROUGHBRED MINING COMPANY, L.L.C.
                            TWENTYMILE COAL COMPANY
                            WILLIAMSVILLE COAL COMPANY, LLC
                            YANKEETOWN DOCK CORPORATION

                            By: /s/ Walter L. Hawkins, Jr.
                                ---------------------------
                                Name: Walter L. Hawkins, Jr.
                                Title: Vice President

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<PAGE>

ADDITIONAL GUARANTORS::

                            DIXON MINING COMPANY, LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

                            DODGE HILL HOLDING JV, LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

                            DODGE HILL OF KENTUCKY, LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

                            DODGE HILL MINING COMPANY, LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

                            HMC MINING, LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

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                            PHC ACQUISITION CORP.

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

                            RANDOLPH LAND HOLDING COMPANY, LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

                            UNION COUNTY COAL CO., LLC

                            By: /s/ Walter L. Hawkins, Jr.
                                -------------------------
                            Name: Walter L. Hawkins, Jr.
                            Title: Vice President & Treasurer

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<PAGE>

                                   SCHEDULE 1

                          NEW GUARANTEEING SUBSIDIARIES

DIXON MINING COMPANY, LLC, a Kentucky Limited Liability Company
DODGE HILL HOLDING JV, LLC, a Delaware Limited Liability
DODGE HILL OF KENTUCKY, LLC, a Delaware Limited Liability
DODGE HILL MINING COMPANY, LLC, a Kentucky Limited Liability Company
HMC MINING, LLC, a Delaware Limited Liability
PHC ACQUISITION CORP., a Delaware corporation
RANDOLPH LAND HOLDING COMPANY, LLC, a Delaware Limited Liability
UNION COUNTY COAL CO., LLC, a Kentucky Limited Liability Company

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