EXHIBIT 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

     We consent to the incorporation by reference in the Registration Statement (Form S-8 No. 333-xxxxx) pertaining to the Arch Coal, Inc. Retirement Plan of our report dated February 23, 2005, with respect to the consolidated financial statements and schedule of Arch Coal, Inc., Arch Coal, Inc. management’s assessment of the effectiveness of internal control over financial reporting, and the effectiveness of internal control over financial reporting of Arch Coal, Inc., included in its Annual Report (Form 10-K) for the year ended December 31, 2004, filed with the Securities and Exchange Commission.

/s/ ERNST & YOUNG LLP
 

St. Louis, Missouri
August 11, 2005