Series 1 includes photographs, portraits, and correspondence collected by Merrill for the above publications. Series 2 through 5 include photographs of groups, particularly of the United States Geological and Geographical Surveys of the Territories (Hayden Surveys); and photographs of geological formations and of buildings in the Washington, D.C. area. Series 6 includes Merrill's professional correspondence as curator at the USNM concerning the exchange and identification of gems and meteorites, expositions and exhibits, and the administration of the USNM and its Department of Geology and Department of Lithology and Physical Geology.
The following lists index correspondence found in the authors' folders in Series 1 and received by James Hall, Ferdinand Vandiveer Hayden, and George P. Merrill. Other correspondence in Series 1 is indexed by both author and recipient in the Archives' computer index. Merrill's professional correspondence in Series 6 is indexed by author.
Correspondence to James Hall: see Charles Baker Adams, Jean Louis Agassiz, Spencer F. Baird, William Thomas Blanford, John Collett, Timothy Abbott Conrad, James Deane, Amos Eaton, John Wells Foster, Augustus Addison Gould, Benjamin Apthorp Gould, William Frank Eugene Gurley, Joseph Henry, Clarence Luther Herrick, John Frederick William Herschel, Clarence King, Increase Allen Lapham, Albert Ripley Leeds, John Peter Lesley, John Locke, Charles Lyell, Beriju N. Martin, Archibald R. Marvine, William Williams Mather, Charles Sedgwick Minot, Elisha Mitchell, John M. Murrish, John Strong Newberry, David Dale Owen, John B. Perry, Benjamin Peirce, William C. Redfield, Henry Darwin Rogers, James Blythe Rogers, Zadock Thompson, John Torrey, Lardner Vanuxem, Charles M. Wheatley and Jeffries Wyman.
Correspondence to Ferdinand Vandiveer Hayden: see Harrison Allen, Joel Asaph Allen, Samuel Aughey, Joachim Barrande, Charles Barrois, William Phipps Blake, William H. Brewer, Thomas Chrowder Chamberlin, Robert Collett, Edward Drinker Cope, Elliott Coues, James Dwight Dana, George M. Dawson, Henry Draper, Frederick M. Endlich, George T. Engelmann, Richard Etheridge, Archibald Geikie, Hanns Bruno Geinitz, George Gibbs, Daniel Coit Gilman, August Radcliffe Grote, Arnold Henry Guyot, Herman August Hagen, Samuel Stehman Haldemann, Charles F. Hartt, George W. Hawes, Oswald Heer, Julius Erasmus Hilgard, Edward Singleton Holden, Joseph Dalton Hooker, Eben Norton Horsford, Alpheus Hyatt, Roland Duer Irving, Samuel William Johnson, August A. von Kollicker, L. de Koninck, John Lawrence LeConte, Joseph Leidy, Joshua Lindahl, George Little, Archibald Liversidge, Chester Smith Lyman, John Lynch, Joseph Vander Maelen, Jules Marcou, Othniel Charles Marsh, Fielding Bradford Meek, Benjamin Franklin Mudge, John Strong Newberry, Henry Newton, Hubert Anson Newton, William Harmon Niles, Richard Owen, John Wesley Powell, Joseph Prestwich, Ferdinand von Richtofen, Charles Valentine Riley, Henry Darwin Rogers, William Barton Rogers, Philip Lutley Sclater, Harry Govier Seeley, Benjamin Franklin Shumard, Benjamin Silliman, Jr., Ainsworth Rand Spofford, Edward Suess, Joseph Szabo, William Petit Trowbridge, Franz Ritter von Havery, William Dwight Whitney, Charles Whittlesey, Alexander Newton Winchell, Amos Henry Worthen and Karl Afred von Zittel.
Correspondence to George P. Merrill: see Cleveland Abbe, Frank Dawson Adams, Wilbur Olin Atwater, A. B. Aubest, Charles Babcock, Ray S. Bassler, Tarleton Hoffman Bean, Charles Emerson Beecher, Albert Smith Bickmore, William Phipps Blake, John Caspar Branner, Garland Carr Broadhead, George Jarvis Brush, Samuel Calvin Giovanni Capellini, Thomas Chrowder Chamberlin, William Bullock Clark, Frank Wigglesworth Clarke, Edward Waller Claypole, Emil Cohen, George Hammell Cook, Edward Travers Cox, Alja Robinson Crook, William Otis Crosby, Charles Whitman Cross, Thomas Nelson Dale, William H. Dall, Edward Salisbury Dana, James Dwight Dana, John William Dawson, David T. Day, Orville A. Derby, Joseph Silas Diller, Edwin Theodore Dumble, Thomas Egleston, George Homans Eldridge, Benjamin Kendall Emerson, Samuel Franklin Emmons, Herman Leroy Fairchild, Edward Holyoke Farrington, Oliver Cummings Farrington, Charles Henry Fernald, Merritt Caldwell Fernald, Lazarus Fletcher, Persifor Frazer, Anton Fritsch, Grove Karl Gilbert, Frank Austin Gooch, George Brown Goode, Leon S. Griswold, Arnold Hague, Christopher Webster Hall, William Hallock, Alfred Harker, Abram Winegardner Harris, George W. Hawes, Robert Hay, Rubit J. Hill, William Herbert Hobbs, Joseph A. Holmes, William Henry Holmes, Joseph Paxson Iddings, John Wesley Judd, Orange Judd, Alexis Anastay Julien, James Furman Kemp, Washington Carruthers Kerr, Karl Kraepelin, Samuel P. Langley, Isaac Lea, John Peter Lesley, Henry Carvill Lewis, Joshua Lindahl, Marshall McDonald, Jules Marcou, Otis Tufton Mason, Frederick James Hamilton Merrill, Mansfield Merriman, Adolf B. Meyer, Edward Williams Morley, Charles Edward Munroe, Edward Francis Baxter Orton, Albert Charles Peale, Richard Alexander Fullerton Penrose, Jr., James Constantine Pilling, Louis Valentine Pirsson, Daniel Webster Prentiss, John Robert Procter, Charles Smith Prosser, Raphael Pumpelly, Rossiter Worthington Raymond, Hans Reusch, William Jones Rhees, William North Rice, Carl Ludwig Rominger, Israel C. Russell, James Merrill Safford, Frank Lamson Scribner, Joseph William Winthrop Spencer, Frank Springer, Timothy Wilson Stanton, Leonhard Stejneger, John James Stevenson, Ralph Stockman Tarr, William B. Taylor, William Petit Trowbridge, Frederick William True, Peter Tscherwinsky, Charles D. Walcott, Henry Augustus Ward, J. E. Watkins, Walter Harvey Weed, James Clarke Welling, Thomas C. Weston, Charles Abiathar White, David White, Theodore G. White, George Huntington Williams, Henry Shaler Williams, J. Francis Williams, Bailey Willis, Thomas Wilson, Alexander Newton Winchell, Henry Woodward and William S. Yeates.