Correlation of the Formations Described in the Fort Apache Region in Arizona with Similar Formations in Other Parts of the State

Abstract

Canyon sections have met with little success.2 As my field work as well as Gilbert's was done before anything much was really known of the geology of that part of Arizona, the sedimentary rocks were mapped and described in groups, as it then appeared impracticable to map them in as great detail as has since proved possible in the Ray quadrangle, for instance. Furthermore, on account of the advanced knowledge of the geology of the entire region, certain peculiar formations which were then difficult to identify can now be readily placed by comparing them with stratagraphic work in other sections. The following sections of the Palaeozoic strata of Arizona from Mexico to the Grand Canyon have been made: Bisbee,4 Tombstone,5 Clifton,6 Globe and Ray Quadrangles,7 Roosevelt,s Southern,9 Part of the Sierra Ancha,10 Northern Part of the Sierra Ancha,1 Head of Canyon Creek,12 Jerome region,13 and Grand Canyon.14 By a comparison of these sections it is easily seen that Gilbert did not see the entire Cambrian series at Canyon creek and that his Tonto Sandstone, as with my sections, is the upper part of the series. His section at the head of Canyon creek was often visited by the writer, and from appearance all he examined at this point was the Dripping Spring quartzite and the Barnes conglomerate; the rest of the series is wanting at this point and the Dripping Spring quartzite is in itself not its full thickness. Gilbert's section is on the crest of the east and west older pre-cambrian ridge that underlies the Palaeozoic here and now extends as the surface rock from near Ellison P. 0. westward through the Tonto basin, covering a region from five to fifteen miles wide. In mapping the formation the writer followed Gilbert and considered the formation below the Barnes conglomerate as Algonkian. But in the light of later investigations it is the lower part of the Cambrian series and is included in the Tonto group of Noble's Grand Canyon section. Several miles down Canyon creek from where Gilbert took his measurements the Pioneer shale comes to view beneath the Barnes conglomerate. The