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Mr. M. R. Campbell; the Lassen Peak sheet and Sacramento sheet in California, the geology of the former by Mr. J. S. Diller, that of the latter by Mr. W. Lindgren. The character of the geology is equally diverse, embracing highly metamorphosed sediments in the first case, slightly modified strata in the second, and in the last two, metamorphosed igneous and sedimentary rocks associated with volcanic lavas. We notice with satisfaction the prominence given to economic features as well as the clear statement of facts regarding the dates at which the work was prosecuted, and the investigators who are to be credited with the work, two essential elements in forming a judgment as to the character of the results.

While the atlas sheets are alike in size they differ in scale from 1-250,000 to 1-62,500. The relative areas, however, are shown upon an index map on the cover of the atlas. These differences of scale are desirable because of the variable importance of the different parts of the country, and the variability in the character of the geology, which may be best represented upon maps of different scales. Such flexibility is a distinct advantage. The success of the effort to introduce greater elasticity into the method of coloring geological formations will be variously estimated. It is not possible to form a fair opinion of the merits of the system from the few examples of it furnished by the four atlas sheets already finished. But it would seem that the prominence accorded to pattern in the system, by making it a basis for the distinction of the main subdivisions of rocks: sedimentary, igneous and metamorphic, has been nullified by the lithographer, who has succeeded so admirably in reducing the lining to a mechanical minimum that the detection and recognition of patterns is a test of eyesight. We appreciate the difficulties attending the application of any comprehensive scheme of colors to so large and diversified a series of atlas sheets as that which will constitute the map of the United States, and look upon the efforts so far made as having advanced the problem without completely solving it. In the meantime the results already obtained by the geologists of the Survey in many