The NUCMC home page is at http://www.loc.gov/coll/nucmc/.
The home page looks like this:
There is a Search box at the top of this page - DON'T USE ONLY THIS!!! It searches only the NUCMC web pages, all Cataloguing Web Pages, and All Library of Congress Web pages.
The actual search for manuscript collections is through the link for "Searching on OCLC WorldCat" under the "Searching Manuscripts" heading in the middle of the page. That page looks like:
The options on this page are to:
1. Simple Search Form (word list) -- titles, notes, and subject fields
2. Simple Search Form (word list) -- all names fields
3. Simple Search Form (left-anchored phrase) -- all names fields
4. Advanced Search Form
? Searching Instructions and Hints
I used the "Simple Search Form (word list) - titles, notes and subject fields" for (without the quotes):
* "seaver" - 359 matches
* "seaver family" - 56 matches
* "seaver diary" - 7 matches
* "seaver letter" - 39 matches
* "seaver genealogy" - 12 matches
Try all of the Search options - they may lead you to a collection that is not found by searching just the Names fields.
As an example of a manuscript collection that might contain significant Seaver family history material:
Author: Seaver family. Title: Papers, 1672-1944, bulk: 1672-1898. Description: 1 narrow box and 1 oversize box. Notes: Papers of the Seaver family of Roxbury, Mass. including deeds and plans for lands in Roxbury and later Colrain, Mass., quitclaims, wills, inventories, and other estate records of Joshua Seaver, his sons Ebenezer (1687-1773), Joshua, Robert, and Jonathan, and Ebenezer's son Ebenezer (1721-1785). Also, Jonathan Seaver's account books (1734-45, 1745-53); a few letters to Ebenezer Seaver (1763-1844); a sketch of the history of New England written for his descendants by Noah Clap; and letters exchanged between Susie (Hibbard) Seaver and her son Henry M. while the latter was travelling in Europe in 1898. Parker, Mary S., Dec. 1925. Some items are individually described in the MHS manuscript catalog. Subjects: Clap family. Account books. Inventories of decedents' estates. Real property -- Massachusetts -- Colrain. Real property -- Massachusetts -- Roxbury (Boston) Voyages and travels. Wills. Europe -- Description and travel. Other authors: Clap, Noah, 1718-1799. Seaver, Ebenezer, 1687-1773. Seaver, Ebenezer, 1721-1785. Seaver, Ebenezer, 1763-1844. Seaver, Henry Morse, 1873-1947. Seaver, Jonathan, 1700-1754. Seaver, Joshua, 1641-1730. Seaver, Joshua, 1678-1739. Seaver, Robert, 1698-1771. Seaver, Susan Hibbard, 1851-1909. Control No.: ocm26827656
Do you think that a descendant of one of these Seaver men would like to see this manuscript collection? Heck, I want to see it!! Where is it?
They cleverly hide how to find out the name of the repository in their Locating Collections page. I followed this trail, which I wrote about three years ago, here. The collection above is at the Massachusetts Historical Society at 1154 Boylston Street in Boston.