Exhibit 10.70

# SIXTH AMENDMENT TOAGREEMENT OF SALE AND
PURCHASE

THIS
SIXTH AMENDMENT TO AGREEMENT OF SALE AND PURCHASE (this Sixth
Amendment) is entered into as of the 27th day of October,
2004, by and between MACK-CALI TEXAS PROPERTY L.P., a Texas limited partnership
(Seller), and CENTENNIAL ACQUISITION COMPANY, a Texas corporation, and
WARAMAUG ACQUISITION CORP., a Texas corporation (collectively,
Purchaser).

A.              Seller
and Purchaser entered into that certain Agreement of Sale and Purchase           dated as
of August 10, 2004, as amended by that certain Amendment to Agreement           of Sale
and Purchase between Seller and Purchaser dated as of October 12,           2004, as
further amended by that certain Second Amendment to Agreement of Sale           and
Purchase between Seller and Purchaser dated as of October 18, 2004, as
          further amended by that certain Third Amendment to Agreement of Sale and
          Purchase between Seller and Purchaser dated as of October 20, 2004, as further
          amended by that certain Fourth Amendment to Agreement of Sale and Purchase
          between Seller and Purchaser dated as of October 21, 2004, and as further
          amended by that certain Fifth Amendment to Agreement of Sale and Purchase
          between Seller and Purchaser dated as of October 25, 2004 (as amended to
          date, the Purchase Agreement). All capitalized
          terms used but not defined herein shall have the meaning given such terms in
the           Purchase Agreement.

B.              Seller
and Purchaser now desire to amend the Purchase Agreement as set forth           below.

NOW,
THEREFORE, for good and valuable consideration, the receipt and sufficiency of which is
hereby acknowledged, Seller and Purchaser agree as follows:

1.    Evaluation
Period.  The expiration of the Evaluation Period           is hereby
extended to 5:00 p.m. Central Time on October 28, 2004.

2.    Reaffirmation.  
Except as modified by this Sixth Amendment,           the Purchase Agreement is hereby
ratified and confirmed and in full force and           effect. In the event of a conflict
between the terms of this Sixth Amendment and           the Purchase Agreement, the terms
of this Sixth Amendment shall control.

3.    Counterparts.  
This Sixth Amendment may be executed in any           number of counterparts, all of
which taken together will constitute one and the           same Sixth Amendment, and the
signature page of any counterpart may be removed           therefrom and attached to any
other counterpart. This Sixth Amendment shall be           legally binding upon receipt
by each party of the facsimile or the original           signature of Seller and of
Purchaser.

[SIGNATURES
FOLLOW ON NEXT SUCCEEDING PAGE]

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IN
WITNESS WHEREOF the parties have executed this Sixth Amendment as of the day and year
first above written.

| |  | PURCHASER:CENTENNIAL ACQUISITION COMPANYBy:  /s/ Steven H. Levin
Name:  Steven H. LevinTitle:  President
| |  | ----------------------------------------------------------------------------------------------------------------------

| |  | WARAMAUG ACQUISITION CORP.By:  /s/  Cindy Nelson
Name:  Cindy NelsonTitle:  Vice President
| |  | --------------------------------------------------------------------------------------------------------

| |  | SELLER:MACK-CALI TEXAS PROPERTY L.P.By:  Mack-Cali Sub XVII, Inc., its general partner
      By:  /s/  Roger W. Thomas            Name:  Roger W. Thomas
      Title:  Executive Vice President                   and General Counsel
| |  | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

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