Total Cretaceous 3,500 feet. The three upper sandstones, the Masuk, the Blue Gate, and the Tununk, are so nearly identical in their lithologic characters that I was unable to discriminate them in localities where their sequence was unknown. This was especially the case upon the summits of Mounts Ellen and Pennell where they occur in a somewhat metamorphosed condition. All of them contain thin beds of coal, none of which are continuous over large areas, and only one of which was observed of workable thickness. At the western foot of Mount Ellen, a bed four feet thick lies at the base of the Blue Gate Sandstone. There is almost equal difficulty in discriminating the Masuk, the Blue Gate, and the Tununk shales. The first is usually of a paler color and is more apt to include arenaceous bands. It has not been found to contain fossils, while the lower shales rarely fail to afford them when search is made. The Blue Gate and Tununk shales are typical examples of fine argillaceous sediments. They are beautifully laminated and are remarkably homogeneous. It is only in fresh escarpments that the lamination is seen, the weathered surface presenting a structureless clay. The fossils of these shales are so numerous, when they have been sought out and studied, that they will probably serve not merely to discriminate the two, but also to correlate them with some of the beds which have been examined elsewhere in the Colorado Basin. For the present I am unable to refer any of the Cretaceous rocks above the Henry’s Fork Group to the divisions which have been recognized elsewhere, and it is for this reason that I have given local, and perhaps temporary names to such beds as I have need to mention in the discussion of the structure of the mountains. The fossils of the Henry’s Fork Group have been more fully collected, and they have been referred without question by Dr. White to the group of that name, as recognized in the Green River Basin (Geology of the Uinta Mountains, pp. 82 and 94). The white grit which lies at the base of the group is a conspicuous bed of unusual persistence, and is recognized wherever Cretaceous rocks are found in the upper basin of the Colorado. _Jura-Trias._—The rocks which intervene between the base of the Cretaceous and the summit of the Carboniferous are of doubtful age, having been referred to the Trias by one geologist and to the Jura and Trias by others, while the fossils recently discovered by Mr. Howell (Geology of Uinta Mountains, page 80) lead to the suspicion at least that they are all Jurassic. It is probable that the uncertainty will soon be dispelled by the more thorough working of Mr. Howell’s new localities; but while it remains, it seems best to recognize its existence in our nomenclature, and I shall include the whole of the doubtful series under the title of _Jura-Trias_. At the Henry Mountains it is easily divided into four groups, as follows: