xcii GENERAL SUMMAKY OF SCIENTIFIC AND 



THE UINTA MOUNTAINS. 

 The lately published researches of Powell on the Colorado give 

 us the details of the geological succession in the Uinta Mountains. 

 The sedimentary groups of what he has called the Plateau Province 

 rest upon a series of Eozoic rocks, to which he has given the name of 

 the Red Creek quartzite, consisting of quartzites, interstratified with 

 hornblendic, chloritic, and micaceous schists, in appressed folds. 

 The thickness of these crystalline schists is provisionally put down 

 at 10,000 feet. Resting unconformably upon these rocks, and hold- 

 ing at its base fragments derived from them, is the Uinta group of 

 sandstones, quartzites, and shales, measuring 12,500 feet in thick- 

 ness, and provisionally regarded by Powell as Devonian. This had 

 suffered great erosion previous to the deposition of the Carbonifer- 

 ous series, and is divided in ascending order into about 400 feet of 

 sandstones, known as the Lodore division, followed by a mass of 

 2000 feet, chiefly of limestone ; above which are the Lower and Up- 

 per Aubrey groups, each 1000 feet in thickness, and both consisting 

 of limestones, with some interstratified sandstones and clierty layers, 

 making thus a total of 4400 feet of rocks of Carboniferous age, rest- 

 ing sometimes on the crystalline schists, and sometimes on the eroded 

 Uinta sandstone. In the Grand Canon of the Colorado, however, 

 the Carboniferous rests in part upon crystalline rocks, which Powell 

 regards, like the Red Creek group, as Eozoic (and which consist 

 of hornblendic and micaceous schists, with beds and dikes of 

 granite), and in part upon what he calls the Grand Canon group 

 of sediments. These consist of about 10,000 feet of sandstones, 

 shales, and limestones, with imperfectly preserved fossils, probably 

 Cambrian, down to the base. Between this group and the Carbon- 

 iferous are about 800 feet of sandstones, shales, and limestones, des- 

 ignated as the Tonto group. These are found to rest upon the 

 eroded basset edges of the lower sandstones ; and being followed 

 conformably by the Carboniferous, were by Powell assigned to the 

 latter period, though, from the presence in it of Cruziana, it has been 

 referred to a lower horizon. In some parts the Tonto group rests di- 

 rectly upon the crystalline schists. 



PALEOZOIC FOSSILS. 



The series above the Tonto group, according to White, includes 

 the Lower Carboniferous, Carboniferous, and Permian; while the 

 Grand Canon strata have yielded as yet but few fossils, among which 

 have been identified only Lingulella and Obolella. In parts of Utah, 

 Nevada, and Arizona he has found trilobites of the genera Olenellus, 

 Conocoryphe, and Agnostus, showing a low Cambrian horizon. The 

 characteristic Crustacea of the Levis limestone are met with in sev- 

 eral localities, and in one place the Phyllograptus of the so-called 



