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degrees to the south a short distance below or to the south <br />of the present quarry. The changes in dip are due to <br />folding and faulting. <br />The limestone being considered is a part of the <br />Leadville formation which outcrops along the northern rim of <br />the Colorado River canyon from Dotsero to Mitchell Creek. <br />In the Leadville and Gilman areas, where the leadville is <br />famous for its ore deposits, it is called limestone although <br />the formation is predominately dolomite with a few interbedded <br />dolomitic limestone beds. True limestone forms the upper <br />half of the Leadville, and it is present as a prominent <br />massive bed in areas to the south and east, as in the Colorado <br />Springs, north of Crested Butte, and north of Glenwood <br />Springs areas. North and west of these areas the limestone <br />pinches out as a result of nondeposition or pre-Pennsylvanian <br />erosion and only dolomite is present in the Leadville series. <br />North of Glenwood Springs the upper part of the <br />Leadville is a massive bed of 100 to 125 feet thick of gray, <br />coarsely crystalline rock composed of 90 to 98 percent <br />calcium carbonate and low in both silica and magnesium <br />carbonate. Comparable limestone of this quality and magnitude <br />is not present in any other horizon of the sedimentary <br />section anywhere in Colorado. Below the massive limestone <br />and in quite sharp contact with it, the lower 100 feet of <br />the Leadville is predominantly dolomite, with some interbedded <br />dolomitic limestone, in which sandy zones and chert stringers <br />and nodules are characteristic. As exposed in cliffs, the <br />massive limestone forms smooth surfaces devoid of bedding, <br />whereas bedding is quite evident in the dolomite below. <br />