PREFATORY NOTE. U. S. GEOLOGICAL AND GEOGRAPHICAL Bulletin No. 4, series of 1877, completes Volume III; and with this. number are issued index, title-page, table of contents, list of illustrations, &c., for the whole volume. It is hoped that the separately published numbers are preserved for binding, as there is no issue of the Bulletins in bound volumes from this office, and as back numbers cannot always be supplied to complete deficient files. In concluding the third volume of Bulletins, a word regarding the origin and progress of this publication will not be out of place. The issue began in 1874, when it was found desirable to establish more ready means of communication with the public and with scientific bodies than the regular Reports of the Survey afforded; the design being to publish, without the delay incident to the appearance of more elaborate and extended articles, such new or specially interesting matter as should be contributed to the general results of the Explorations under my charge by the members or the collaborators of the Survey. The practical importance of prompt measures in such cases is well recognized, and sufficiently attested by the success which the Bulletins have achieved. The First and Second Bulletins, which appeared in 1874, are separately paged pamphlets, without ostensible connection with each other or with subsequent ones, but together constituting a "First Series" of the publication. Bulletins which appeared in 1875, being those of a "Second Series" and six in number, are continuously paged. With No. 6 were issued title, contents, index, &c., for all the numbers of both "series " which had then appeared; the design being that these should together constitute a Volume I, in order that the inconvenient distinction of "series" might be dropped. With Bulletin No. 1 of 1876, the publication was established as an annual serial; the four consecutively paged numbers of that year constituting Volume II. The four Bulletins of 1877 constitute Volume III, which compares favorably with its predecessors in the extent, variety, and importance. of its contents, and is greatly improved in typography and general appearance. Should no unforeseen circumstance prevent, the Bulletins will continue |