April 21, 2010



Securities and Exchange Commission
100 F Street NE
Washington, D.C.  20549


             Re: Claymore Securities Defined Portfolios, Series 680

        Closed-End Income & Treasury Limited Duration Portfolio, Series 7

                               File No. 333-165207

--------------------------------------------------------------------------------

Ladies and Gentlemen:

     On behalf of Claymore Securities, Inc., depositor, sponsor and underwriter
of the Claymore Securities Defined Portfolios, Series 680, consisting of the
above-captioned trust (the "Trust"), there is enclosed Amendment No. 1 to the
Registration Statement on Form S-6 relating to securities of Claymore Securities
Defined Portfolios, Series 680 (the "Fund").

     The Reference Trust Agreement was entered into by Claymore Securities,
Inc., as Depositor, and The Bank of New York Mellon, as Trustee, on the date
hereof, and Securities (or delivery statements relating to contracts for the
purchase thereof) in the aggregate amount of the portfolio(s) have been
deposited with the Trustee. In connection therewith the Trustee is prepared to
establish book entry positions which are being retained by the Trustee for
delivery after the effectiveness of the Registration Statement.

     In addition to Amendment No. 1, the exhibits listed therein are submitted
herewith.

     Except as indicated in the Memorandum of Changes, the changes in the
Prospectus represent primarily the completion of various statements regarding
the Securities deposited in the Trust and the dates of record, deposit,
distribution, termination and evaluation, together with a list of the Securities
which will comprise the portfolio of the Trusts, the Statement of Financial
Condition of the Trusts and the Report of Independent Registered Public
Accounting Firm.

     We have appreciated the courtesy and cooperation of the members of the
Staff and if there are any questions on which we may be of assistance, please do
not hesitate to call either Eric F. Fess (312-845-3781) or Morrison C. Warren
(312-845-3484) collect.

                                                               Very truly yours,

                                                      /s/ Chapman and Cutler LLP
                                                      --------------------------
                                                          CHAPMAN AND CUTLER LLP