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96 of his discoveries—Mather, Emmons, and Vanuxem. It has given existence to publications that have become classic (1836 to 1842). By the side of these promoters who have the merit of having been the first to conquer the greatest difficulties, justice demands that there should be written the names of two geologists not attached officially to the service of the United States, whose powerful influence ought to be proclaimed. Our compatriot De Verneuil pursued since 1846, with the success that is well known, a task which no other could better undertake, that of comparing upon the two continents all the sedimentary deposits, from the most ancient down to those that contain the coal; and Dana, by his original work and by his excellent books, has contributed singularly to the education of all those who, in Europe as well as in America, devoted themselves and still devote themselves to the study of geology and mineralogy.

The first results attained proved the utility of like enterprises. Thus, following the steps of the local governments, the Federal Government entered into the same path.

It was at first for the great Territories of the West, little known and not yet classed as independent States. The wise geologist Hayden, to whom this study was confided and of whom we deplore the loss, worked there with ardor during a dozen years. First of all had to be adopted a rational plan for an exploration at the same time geographic and geologic. This new service bore, indeed, the title of Geological and Geographical Survey of the Territories. Then followed the discovery in 1871, and the detailed exploration in 1872, of the region of the geysers of the Yellowstone; from 1873 to 1879 the complete topographic and geologic survey of the Alpine part of the Rocky Mountains comprised in the State of Colorado. The atlas which unites all these researches (1877) is a chef-d'œuvre of cartography; it is in great part the work of Mr. Holmes, the artist-geologist, of whom one admires the incomparable sketches scattered in profusion through the official publications.

In order to explore the Rocky Mountains (1869 to 1875), Mr. J. W. Powell descended by water the celebrated and dangerous canons of the Colorado, and made a report which has become classic on the phenomena of erosion. During the same epoch Mr. Gilbert made an extremely remarkable study of the Henry Mountains.

At the same time the Engineer Department of the United States Army was charged with work of the same class over an immense country still little more than desert and very little known. The title of this new service, "Geological and geographical exploration and survey of the one hundredth meridian," shows that, in this case also, the examination of the constitution of the