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series with inclusive volumes and dates are given. Definite classes of material are omitted, as follows:

(a) Manuscripts.

(b) Federal, state and city documents with the exception of a few rare items of great historical importance, not easily found in the readily available lists and indexes.

(c) "Periodicals published in the region, except those de- voted mainly or wholly to history. Serials, however, as year- books and publications of societies have been included as a part of the institutional history of the Pacific Northwest."

(d) "Maps, except those independently issued and bound in book form."

Even of the material included in general, there has been more rigid limitation, in order to keep the checklist within reasonable bounds. For example, directories published after 1900 are omitted ; some of the more recent advertising material is excluded; different imprints of the same book are left out unless they are definitely different editions.

The checklist has both the advantage and disadvantages of a co-operative undertaking. It is already proving its useful- ness to the research worker by indicating in just which libraries books and editions are available. Even though limited to printed items in these few libraries, it is quite a full bibli- ography of the important works dealing with this region and will prove especially valuable to libraries as a buying list. We find that individual collectors are referring to it also.

A defect inseparable from co-operative undertakings is that each library probably contains many items listed but not cred- ited to that library. This difficulty arises in various ways. A library having a strong collection rates as unimportant items which are of a great deal of value in a smaller library. Again, the understanding of the limitations of the scope of the work unavoidably differs with the individual and one will list ma- terial which to another seems outside the range of work. An example of this is the Bulletins of the U. S. Geological Survey, some of which are listed in only one or two libraries while they are probably in every library. Still another reason is