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                                                                     EXHIBIT 4.8

                           SPLITROCK SERVICES, INC.,

                                   as Parent

                                      and

                       HARRIS TRUST COMPANY OF NEW YORK

                                  as Trustee

              __________________________________________________


                         FIRST SUPPLEMENTAL INDENTURE

                         Dated as of November 24, 1999

                                 to INDENTURE

                           Dated as of July 24, 1998


              __________________________________________________

                                 $261,000,000

                         11 3/4% Senior Notes due 2008
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     FIRST SUPPLEMENTAL INDENTURE, dated as of November 24, 1999, by and between
SPLITROCK SERVICES, INC., a Delaware corporation, (the "Company"), and HARRIS
TRUST COMPANY OF NEW YORK (formerly THE BANK OF MONTREAL TRUST COMPANY), a New
York banking corporation trust company, as Trustee (the "Trustee").

                                  WITNESSETH
                                  ----------

     WHEREAS the Company has heretofore executed and delivered to the Trustee an
Indenture dated as of July 24, 1998 (the "Indenture"), providing for the
issuance of an aggregate principal amount of up to $311,000,000 of 11 3/4%
Senior Notes due 2008 (the "Securities");

     WHEREAS, the Company has commenced a solicitation of consents (the "Consent
Solicitation") from the Holders to certain amendments to the Indenture as set
forth in the Consent Solicitation Statement of the Company dated November 9,
1999, as amended by a Supplement thereto, dated November 19, 1999, (the
"Proposed Amendment");

     WHEREAS, pursuant to the Consent Solicitation, the Holders of at least a
majority in aggregate principal amount of the Securities outstanding have
consented (the "Requisite Consents") to the amendments effected by this First
Supplemental Indenture in accordance with the provisions of the Indenture;

     WHEREAS, the First Supplemental Indenture evidences the Proposed Amendment
described in the Consent Solicitation Statement and the Supplement thereto;

     WHEREAS, Section 9.02 of the Indenture provides, among other things, that
with the written consent of Securityholders holding not less than a majority in
principal amount of the Securities then outstanding, the Company may from time
to time amend or supplement the Indenture, subject to certain exceptions
specified in Section 9.02 of the Indenture;

     WHEREAS, on November 9, 1999, the Company mailed or otherwise delivered a
Consent Solicitation Statement to each Holder of record as of November 8, 1999
and a Supplement thereto on November 19, 1999, and has obtained the Requisite
Consents;

     WHEREAS, this First Supplemental Indenture has been duly authorized by all
necessary corporate action on the part of the Company; and

     WHEREAS, the Company has delivered, or caused to be delivered, to the
Trustee, an Officer's Certificate and an Opinion of Counsel meeting the
requirements of Section 11.04 and 11.05 of the Indenture and stating that all
conditions precedent and covenants, if any, provided for in the Indenture
relating to this First Supplemental Indenture have been satisfied.

     NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, receipt of which is hereby acknowledged, the Subsidiary
Guarantor, the Company, and the Trustee mutually covenant and agree for the
equal and ratable benefit of the holders of the Securities as follows:

                                       1
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                                   ARTICLE I
                                   ---------

                                  Amendments
                                  ----------


     SECTION 1.01.  Amendments to Indenture and the Securities. The amendments
                    ------------------------------------------
set forth in this First Supplemental Indenture shall become operative on the
date that the Company notifies the Trustee in connection with the Consent
Solicitation that the Consents tendered are accepted pursuant to the Consent
Solicitation (the "Consent Date"). If Holders of a majority in aggregate
principal amount of the Securities do not tender Consents (the "Requisite
Consents") for any reason and the Consent Solicitation is not effected, the
amendments set forth herein will not become operative. The Indenture is hereby
amended as follows:

               A.   From and after the Consent Date, Clause (b)(vi) of Section
     4.03 of the Indenture is hereby amended by deleting the words "80% of" just
     before the phrase "(a) the Fair Market Value" therein.

               B.  From and after the Consent Date, the defined term "Purchase
     Money Indebtedness" in Section 1.01 of the Indenture is hereby amended by
     deleting clause (iii) thereof in its entirety and inserting the following
     in its place: "(iii) with respect to any Secured Indebtedness which
     constitutes Purchase Money Indebtedness, the Stated Maturity of such
     Secured Indebtedness shall not exceed the expected depreciable life, as
     determined by the Company, of the Telecommunications Assets securing such
     Secured Indebtedness."

     SECTION 1.02. Successors and Assigns.  This Article I shall be binding upon
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the Company and shall inure to the benefit of the successors and assigns of the
Trustee and the Holders and, in the event of any transfer or assignment of
rights by any Holder or the Trustee, the rights and privileges conferred upon
that party in the Indenture and this First Supplemental Indenture and in the
Securities shall automatically extend to and be vested in such transferee or
assignee, all subject to the terms and conditions of the Indenture and this
First Supplemental Indenture.

     SECTION 1.03. Modification.  No modification, amendment or waiver of any
                   -------------
provision of this Article 1, nor the consent to any departure by the Company
therefrom, shall in any event be effective unless the same shall be in writing
and signed by the Trustee, and then such waiver or consent shall be effective
only in the specific instance and for the purpose for which given.

                                       2
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                                  ARTICLE II
                                  ----------

                                 Miscellaneous
                                 -------------

     SECTION 2.01.  Ratification of Indenture: Supplemental Indentures Part
                    -------------------------------------------------------
of Indenture.  Except as expressly amended hereby, the Indenture is in all
-------------
respects ratified and confirmed and all the terms, conditions and provisions
thereof shall remain in full force and effect. Upon the execution and delivery
of this First Supplemental Indenture by the Company and the Trustee, this First
Supplemental Indenture shall form a part of the Indenture for all purposes, and
every holder of Securities heretofore or hereafter authenticated and delivered
shall be bound hereby. Any and all references, whether within the Indenture or
in any notice, certificate or other instrument or document, shall be deemed to
include a reference to this First Supplemental Indenture (whether or not made),
unless the context shall otherwise require.

     SECTION 2.02.  Governing Law; Governance, Etc. THIS FIRST SUPPLEMENTAL
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INDENTURE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF
THE STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF
CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION OF THE LAWS OF ANOTHER
JURISDICTION WOULD BE REQUIRED THEREBY. This First Supplemental Indenture shall
be governed and construed in accordance with the applicable terms and provisions
of the Indenture as amended hereby, which terms and provisions are incorporated
herein by reference, as if this First Supplemental Indenture were the
"Indenture" referred to therein.

     SECTION 2.03.  Trustee Makes No Representation.  The Trustee makes no
                    --------------------------------
representation as to the validity or sufficiency of this First Supplemental
Indenture.

     SECTION 2.04.  Counterparts.  The parties may sign any number of copies of
                    -------------
this First Supplemental Indenture.  Each signed copy shall be an original, but
all of them together represent the same agreement.

     SECTION 2.05.  Effect of Headings.  The Section headings herein are for
                    -------------------
convenience only and shall not effect the construction thereof

     SECTION 2.06.  Terms.  Certain capitalized terms used but not defined
                    ------
herein have the meanings assigned to them in the Indenture.

     SECTION 2.07.  Entire Agreement.  This First Supplemental Indenture,
                    ----------------
together with the Indenture as amended hereby and the Securities, contains the
entire agreement of the parties, and supersedes all other representations,
warranties, agreements and understandings between the parties, oral or
otherwise, with respect to the matters contained herein and therein.

     SECTION 2.08.  Benefits of First Supplemental Indenture. Nothing in
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this First Supplemental Indenture, the Indenture, or the Securities, express or
implied, shall give to any Person, other than the parties hereto and thereto and
their successors hereunder and thereunder, and the Securityholders, any benefit
of any legal or equitable right, remedy or claim under the Indenture, the First
Supplemental Indenture or the Securities.

                                       3
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     IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental
Indenture to be duly executed as of the date first above written.


                                   SPLITROCK SERVICES, INC.



                                   By_____________________________________
                                   Name:
                                   Title:

                                   HARRIS TRUST COMPANY OF NEW YORK,
                                   as Trustee,



                                   By ____________________________________
                                   Name:
                                   Title:

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