the rate of accumulation of muds, sands and pebble beds, and of the formation of limestones, in relation to each other and under varying conditions, and the detection of the marks in the strata recording the conditions incident to the varying rates of accumulation. Until the evidence is fuller the time - ratios of Dana may be adopted as expressing approximate values for the various geological ages.

In all these studies in which the geological time-scale is applied to the evolution of the earth and its inhabitants, the time concerned is not human chronology but is what may be called geochronology. For this purpose we need a standard time- unit. or geochrone. The geochrone applied in Dana's time- ratios appears to be 8,000 feet of sedimentary deposits, as in the Potsdam, (7000 feet sediments and 200 limestone). Something more definite is needed and one in which the equivalents in different kinds of deposit and in different regions can be studied and compared with some approach to accuracy. The Eocene period, as expressed in the gulf states on both sides of the Mississippi river, might be selected as a convenient and practicable standard for this purpose. Humphrey and Abbot's elaborate studies of the Mississippi river furnish minute data for comparison with recent conditions. There are 3,000 feet of marine beds referred to the Eocene in southern Europe. The Eocene or early Tertiary fresh-water beds reach a thickness of at least 10,000 feet. The Tertiary beds in Liguria are estimated to reach the thickness of 23,600 feet. If for the present we assume the Eocene geochrone to be equivalent to the maximum deposit of 3,000 feet of fragmental sediment on the edge of the continent, using Dana's estimates of time-ratios with some modifications, and adopting the term Eocene as the American students of marine Eocene apply it, the following standard time-scale for geochronology is constructed. The geochrone in this scale is the period represented by the Eocene, as understood in North America to include the marine deposits and their faunas, from the close of the Cretaceous to the top of the Vicksburg or white limestone of Smith and Johnston, 1,700 feet of which are seen in Alabama. In England it

may include the Oligocene to the top of the Hempstead beds. I realize that such a proposition furnishes many points for dispute. The scale is open for correction, and the standard may be defined with greater precision. But it is offered as a working hypothesis, to aid and stimulate investigation.

Such a standard time-scale of geochronology, on the basis of the Eocene period for a time-unit or geochrone would read as follows:

The proximity of the Eocene of the Gulf border to continental conditions now in operation, the abundance of its marine fauna for comparison with like faunas of earlier or later age and of the same or different habitats, and its inclusion of traces of land-life for correlation with other conditions, and, in general, the wide distribution of available Eocene deposits and faunas for comparative study, are reasons for calling attention of investigators to this particular field for minute investigation in perfecting the geological time - scale.

HENRY S. WILLIAMS.

EDITORIALS.

THE United States Geological Survey is to be congratulated upon the appearance of the first atlas sheets of the geological map of the United States which, although still considered as preliminary to the regular edition, may be taken as essentially finished, and as embodying the chief features which will characterize the completed work. Each atlas consists of one portion of the whole map printed in four ways: one presenting the topography by itself; one, the areal geology; another, the geological structure by means of cross sections, and a fourth, the features of economic importance. Accompanying these are sheets of text, one of which explains certain elementary concepts of the science and defines the sense in which some of the more common terms are to be employed throughout this series of publications. The text describing the special area surveyed is admirably prepared to set forth in a concise manner the leading features of the geology and of the economic resources. It is prefaced in some cases by a general sketch of the region immediately surrounding the area published, which aids materially the comprehension of the more local geology. In one instance, however, the sketch embraces nearly the whole eastern portion of the United States, which seems unnecessary since, we assume, it is not the intention of the Survey to do away with the publication of its monographs and bulletins, where the full results of the several investigations should appear. Otherwise, the text accompanying the atlas sheets would be insufficient.

The sheets finished are from widely separated parts of the country the Hawley sheet in Massachusetts, the geology of which is by Professor B. K. Emerson; the Kingston sheet in Tennessee, the geology by Mr. C. Willard Hayes, assisted by

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

298

parts of the country should be published without waiting longer for a perfect method of coloring to be devised.

J. P. I.

Or are

Do oscillations of the crust progress by waves? they limited to non-progressive vertical elevations and depressions, or to oblique thrusts and resiliences? Or are there both stationary and progressive oscillations?

The subject does not seem to have received much definite investigation, although it finds incidental expression here and there in geological literature. It is clear, however, that a determination of the stationary or progressive character of crust oscillations must have an important bearing upon the various hypotheses that concern the relations of the earth's crust to its interior. It is obvious that preliminary to a study of these problems there must be dismissed from consideration those merely apparent oscillations of the crust that are in reality but variations of the sea level. It seems quite certain, however, that when these are eliminated there remain a large class of true crustal movements. The elucidation of these is extremely difficult and would be greatly aided if it were known whether they are local or migratory, and, if migratory, whether there are any general laws governing the direction of their movements, their rate of progress, etc. If migratory, do these undulations radiate from a point of origin in all directions, like the wave circles induced upon a liquid surface, or do they, like tidal waves, creep forward in a single direction?

If we combine by free hypothesis the elevations and depressions of the Pacific coast during the Pliocene and Pleistocene times with those of the Mississippi basin and of the Atlantic coast, it is not difficult to construct a procession of elevations and depressions creeping successively across the continent. Is such

a synthesis supported by any close definite data indicating progressive undulation, or is it merely an artificial combination of selected data thrown into order arbitrarily at the suggestion of an hypothesis? This illustrates a class of questions whose solution presumably leads back to crustal and sub-crustal agencies.