Section VIII-3: Presiding officer in case of impeachment - Presentation of impeachment.

  When sitting as a Court of Impeachment, the Senate shall be
presided over by the Chief Justice, or if he is absent or
disqualified, then one of the Associate Justices of the Supreme
Court, to be selected by it, except in cases where all the
members of said court are absent or disqualified, or in cases of
impeachment of any Justice of the Supreme Court, then the Senate
shall elect one of its own members as a presiding officer for
such purpose.  The House of Representatives shall present all
impeachments.