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<br />690
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<br />G, E, UNT'ERMANN AND B, R, UNTERMANN
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<br />The Uinta Mountain group crops out chiefly aloug the crest of the main Uinta
<br />arch, and occurs in the smaller folds only where erosion has exposed it in the
<br />deeper parts of canyons, and along the dissected upthrown sides of fa)llts,
<br />Like the Algonkian, the Cambrian beds are also exposed in the deeppr canyons
<br />and along some of the faults, Such an exposure is found in Jones Hole along the
<br />Island Park fault, Here the Cambrian (Lodore formation) consists of approxi-
<br />mately 400 feet (maximvm for the Monument) of white to red predominantly
<br />coarse quartzitic sandsto!,es at the top, middle, and base of the formation, and
<br />with thin sericitic silty sh~le partings, The middle sandstone member is extremely
<br />glauconitic in part, The: base of the upper sandstone contains casts of small
<br />trilobites, cbiefly the cephaions, Separating these sandstone layers are two princi,
<br />pal sericitic silty shale beds, predominantly green in color, and containing thin
<br />sandstones, some of which are glauconitic. In the spring of 1945, the writers
<br />found a few trilobites il;1 the upper part of the top shale which has a thickness of
<br />60 feet, Although not identifiabie specifically, these forms were considered by
<br />G, Arthur Cooper and Cl;1ristina Lochman' as Upper Cambrian in age, and thus
<br />the Lodore formation may be assigned to this period, The writers are still seeking
<br />better material. Small shell forms resembling BiIlingsell'a and Dicellomus (brachi- ,
<br />opods), specimens of Hyolithes (pteropod), and one form resembling tiny coiled
<br />gastropods are common in some sandy layers throughout the upper half of the
<br />formation, A brownish black shell-stone layer, 1-2 inches thick, occurs midway in
<br />the upper shale, Also, structures similar to "Cruziana" (an undetermined organ-
<br />ism) and "Pateophycus" (seaweed-like impressions) occur in the green and red
<br />silty shales, Mud cracks a:nd ripple marks are abundant, The upper 45 feet of the
<br />basal sandstone member ~ontains 28 feet of red to white "vermicelli" sandstone
<br />with some purple and green sericitic, and ripple-marked shale partings, The
<br />spaghetti-like rods may rhpresent concretions or casts of worm borings,
<br />Other very well represented systems are Mississippian, Pennsylvanian, Per-
<br />mian, Triassic; Jurassic, itnd Cretaceous. Formations representing these periods
<br />are widespread and well distributed throughout the Monument. Absence of Or-
<br />dovician, Silurian, and Devonian beds suggests non-deposition inasmuch as the
<br />basal layers of the Madi~on contain sandy streaks which resemble material in
<br />the upper part of the Lo~ore form,ation. This material consists of poorly sorted
<br />clear to pink quartz graIns concentrated along minute ripple-marked surfaces
<br />and cross-bedding planesi The presence of these sand grains in the basal layers
<br />of the Madison suggests derivation, in part, from the Lodore on which they rest,
<br />No pronounced erosional: unconformity has been observed between the Lodore
<br />and Madison, although a great time break occurs between the two formations,
<br />'Except for the somewhat sandy limestone at the base of the Madison beds,
<br />(Lower Mississippian), the rest of the formation in this area consists chiefly of
<br />massive, cliff-forming, me~ium to coarse dolomites and limestones, some of which
<br />contain pink to black and white banded chert, Some of the dense, tan limestone
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<br />f Personal communication. i
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