specially indebted to Professor Simonin, the author of La Vie Souterraine, and has relied upon him for many facts and figures, especially in reference to the coal mines of France and other countries. Numerous books of travel have been examined, files of newspapers have been searched, and many individuals, familiar with subjects which it was proposed to treat, have been consulted in the author's wanderings after light. He trusts that his labors will not prove to have been in vain.
Several literary gentlemen have aided the author in his enterprise. He is permitted to mention, as among these, Mr. Junius Henri Browne, of New York, and the late Colonel Albert S. Evans, of San Francisco.
In preparing the matter for the press, it has been found convenient to make use of words borrowed from the French and other languages, and also of terms more or less technical in their character. They are not numerous, and are so well understood either by context or by popular use that a glossary is not considered necessary.
The author takes this opportunity to thank the newspaper press and the public for the generous reception accorded to his previous publications, and, in the language of the business card of the period, he hopes to merit a continuance of the same.