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The Green River formation is a series of lake beds of middle :Eocene age which occupies two large intermontane basins, one in Colorado and Utah, the other in Wyoming. The formation averages about 2,000 feet in thickness and covers an area of more than 25,000 square miles. Many of its beds of marlstone, oil shale, and fine-grained sandstone contain varves. As the origin of these varves is closely linked with the climate the writer has attempted rough quantitative estimates of several elements of the climate of the Green River epoch. These esti mates are based largely upon the relative area of the lake and its drainage basin. A climate is 'postulated which was char acterized by cool, moist winters and relatively long, warm Bummers. Presumably the temperature fluctuated rather widely from a mean annual temperature that was of the order of 65 0 F. The rainfall varied with the seasons and probably also fluc tuated rather widely from a mean annual precipitation between 30 and 43 inches.One type of varve predominates. This consists of a pair of laminae, one of which is distinctly richer in organic matter than the other. The contacts between the two parts of the varve and between successive varves are generally sharp. The varves differ considerably in thickness according to the type of rock in which they occur and range from a minimum of 0.014 millimeter in the beds of richest oil shale to about 9.8 milli meters in the beds of fine-grained sandstone. The average thickness of the varves, weighted according to the quantity of ·each type of rock in the formation, is about 0.18 millimeter.The assumption that the pairs of laminae are varves is tested, fir::;t, by analogy with the varves in the deposits of modern lakes and, second, by calculation of the thickness of annual laminae to be expected in the ancient Green River Lake based upon data of present stream loads.The bipartite character of the varves is explained by postu . lating a more or less continuous sedimentation of mineral and organic constituents, with first a peak in the production of the carbonates and then a peak in the production of the plankton, both peaks apparently occurring during the summer, and by assuming that the primary difference in composition was accen tuated by the differential settling rates of the two principal constituents. The preservation of the varves suggests that the lake water was thermally stratified and that the lake may not have been more than 75 or 100 feet deep where the varved deposits accumulated. Three cycles of greater length than the varve cycle are sug gested by fairly regular recurrent variations in the thickness of the varves and in the thickness and character of certain b.eds and by the fairly regular spacing of certain salt-mold layers. The first of these cycles averaged a little less than 12 years in length and appears to correspond to the cycle of sunspot num bers. The second cycle had an average length of about 21,600 years and suggests the average period of about 21,000 years which is the resultant of the cyclic...

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the east end of the range. But soon thereafter it was captured by Lodore Branch, a tributary to the ancestral Cascade Creek, which drained Summit Valley, and so came to flow • along the present site of Lodore Canyon. The steps in this diversion are shown diagrammatically in plate 42. The course of the Green River through Lodore Canyon was formerly regarded as perhaps having been established by superimposition from the Browns Park formation rather than by piracy. Along Bl~cks and Smith Forks of the Green River are remnants of tvi:o Pleistocene erosion surfaces. The older of these, the Tipperary surface, is about 150 feet below the Bear Mountain surface, and the younger, the Lyman surface, is 50 to 75 feet below the Tipperary. Both, however, merge upstream with the present flood plains, and each has a series of treads at its north end, which are explained as partial flood plains abandoned one after another as the stream was captured at successive short intervals upstream by the tributaries of larger streams in adjacent strike valleys. The process by which certain gravel-capped badland escarpments migrate and behead small, asymmetric, gravel-capped alluvial cones is described and illustrated. Only those moraines that gave promise of clarifying the relations between the erosional history and the glacial history • were studied. Bulky terminal moraines on remnants of the Bear Mountain surface in two or three localities north of the Utah-Wyoming boundary line seem to indicate rather clearly a third glacial stage older than the two heretofore recognized in the Uinta Mountains. The three glacial stages-Little Dry (oldest), Blacks Fork, and Smith Fork-appear to be the respective equivalents of Blackwelder's Buffalo, Bull Lake, and Pinedale stages in the Wind River Range. The possible causes of the erosion interval between the Gilbert Peak and Bear Mountain surfaces are examined, but the evidence is inconclusive. The erosion intervals between the Bear Mountain surface and Tipperary surface and between the Tipperary and Lyman surfaces are probably to be linked with the full, strong streams that existed during or just after the corresponding glacial stages. The two youngest surfaces themselves were probably cut by lateral planation of the streams during the somewhat more arid interglacial stages.