March 17, 1998

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                                                                    XXXXXXX X

                                 Xxxxx 00, 0000



Xxxxxxxxx, Inc.
0000 Xxxxx Xxxxxx, Xxxxx 00000
Xxxxxxx, Xxxxx 00000-0000



Attention:        President and Chief Executive Officer

         Reference is made to the Agreement and Plan of Merger between Medusa
Corporation ("Company") and Southdown, Inc. ("Parent") dated March 17, 1998 (the
"Agreement"), which provides for the merger of a subsidiary of Parent with and
into the Company (the "Merger"). The undersigned is the beneficial owner (as
that term is defined in the Agreement) of ______________ common shares (the 
"Shares") of Company and has supported and encouraged the decision by Company 
to execute the Agreement and to consummate the Merger.

         In that connection, and as an inducement to, and in further
consideration of, Parent's entering into the Agreement, the undersigned hereby
grants the irrevocable proxy provided in paragraph (i), and further covenants
and agrees to the matters set forth in paragraphs (ii) through (v) below:

         (i) In consideration of Parent's entering into the Agreement, the
undersigned, being the beneficial owner of _____________ Shares, hereby
irrevocably appoints and constitutes Xxxxxxxx X. Xxxxx and Xxxxxxx X. Xxxxxxx 
as proxies for the undersigned, with full power of substitution, to vote such
Shares, and any other Shares beneficially owned at the time by the undersigned,
at any regular or special meeting of the stockholders of the Company at which
the adoption of the Agreement is to be voted upon, in favor of adoption of the
Agreement. The proxy granted hereby is irrevocable and coupled with an interest.
    
        (ii) The undersigned will not directly or indirectly (A) solicit,
initiate or encourage the submission of any Alternative Proposal (as defined in
the Agreement) with respect to the Company, (B) enter into any agreement with
respect to any Alternative


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Southdown, Inc.
March 27, 1998
Page 2

Proposal with respect to the Company, or (C) participate in any discussion or
negotiation regarding, or furnish to any person any information with respect to,
the making of any proposal that constitutes, or may reasonably be expected to
lead to, any Alternative Proposal with respect to the Company; provided,
however, that the foregoing clause shall not prohibit the undersigned who serves
as a director, officer or employee of the Company from taking any action
(subject to Section 5.3(d) of the Agreement) solely in such capacity.

         (iii) The undersigned agrees, for the term of this agreement, not to
sell, convey or dispose of any Shares other than in connection with the Merger.

         (iv) The undersigned agrees to sign the affiliate letter in the form
attached as Exhibit B to the Agreement, as provided in the Agreement.

         (v) The proxy provided hereby, and the covenants and agreements
contained herein, shall terminate on the earlier of the date (i) that the
Agreement is terminated for any reason other than pursuant to Section 7.1(g),
and (ii) the date set forth in Section 7.1(c) of the Agreement, as such date may
be modified by Company and Parent.



                                             Very truly yours,

                                             [Shareholder]