AUTHOR’S PREFACE. 
Before undertaking the preparation of this Guide for the Carnegie Institu- 
tion of Washington I had spent five summer vacations in the archives of 
Mexico in personal work and in the interest of the School of History of the 
University of Texas. This time was mainly devoted to the Archivo General 
y Publico and the Museo Nacional, and to a search for material for a rela- 
tively restricted portion of United States history. In addition to the time 
thus spent in acquiring preparatory experience and information, sixteen 
months’ work has been done in Mexican archives directly in the interest of 
the Guide; fifteen of these months were spent consecutively between June, 
1907, and October, 1908; another month was devoted to the work in the 
summer of 1909. In addition, brief investigations were made in several 
places in northern Mexico during two short visits in 1911 and 1912. 
To say that I am conscious of many shortcomings in the results of my work 
is unnecessary. But some of them, it is believed, were inevitable under the 
circumstances. The task was absolutely a pioneer one, scarcely a tree having 
been blazed along the way. In only a single one of the many repositories 
examined was a printed list or catalogue of materials found, while such manu- 
script inventories as are kept in other archives are often of very little assist- 
ance to historical investigation. Probably more than half of the working 
hours spent in the archives were devoted to the purely physical tasks of search 
for and handling manuscripts. Many additional hours were consumed in the 
presentation of credentials and the gaining of admission to the various re- 
positories visited. In the remaining time it was necessary to ascertain the 
nature of the contents and to formulate descriptions of the hundreds of 
thousands of more or less unclassified documents which appeared to fall 
within the scope of the Guide. In some cases the desired data could be readily 
gained from the labels of the bundles or volumes or from the cardtulas (title- 
pages) of individual papers; but in many others it was necessary, in order to 
formulate the descriptions, to turn over, one by one, hundreds of miscel- 
laneous documents in a single bundle, and even to read the whole text of 
difficult manuscripts. Besides the difficulties presented by the great mass and 
the miscellaneous character of the materials, there was the inevitable circum- 
stance that the knowledge of one worker could not extend to all of the sub- 
jects presented in the multifarious documents. As a result of these condi- 
tions some of the groups of materials are described here in terms which, to a 
person looking for a specific document, may seem disappointingly general. 
In other cases the more detailed work of specialists will disclose errors of 
judgment or of emphasis in the description of given groups of papers. Rare 
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