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Show 200 GEOLOGY OF THE HIGH PLATEAUS. territory with splendid exposure, and have in many places been thoroughly protected from destruction since early Miocene time at least, but nowhere have they been seen to be covered with any more recent sedimentary formations, excepting the local beds of volcanic sand. It is not probable that every vestige of such a formation, had it existed, should have been so completely destroyed, nor that an erosion of such magnitude should have been withal so uniform as to stop everywhere at the summit of the very perishable limestone which forms the uppermost member of the Bitter Creek. Here, as elsewhere, the volume of Cretaceous beds is very great, probably attaining more than 4,000 feet. The valleys and gorges which, reveal them descend to the westward, while the rocks dip at varying angles to the eastward; thus in the course of 5 or 6 miles the water-courses pass through the entire series. The Cretaceous mass is composed of alternating sandstones and dark-gray shales, which are usually very heavily bedded, uniformly stratified, and have strong and persistent lithological characters. The subdivision of the Cretaceous rocks and their correlation with those of the Plateau Province at large I have not attempted; the study of them has been too superficial and the number of fossils collected is much too small, while the series itself is enormous and highly variable. It is evident at once that, though the series as a whole possesses the same general characteristics as prevail elsewhere, it is very inconstant in details, and comparatively few of the subordinate members can be strictly correlated over extended intervals. The great beds of shale are the most striking members, attaining many hundreds of feet of thickness, with slight interruptions of arenaceous layers, which hardly mar the uniformity of their aspect. Coal of good quality is found in workable beds in the lower half of the series. There is a strong family likeness in all the Cretaceous exposures of the Plateau Province, and their features are as characteristic of the formation as the peculiarities of the Trias; but the wonderful persistence over great areas which marks the Triassic members cannot be affirmed of the Cretaceous. No series of rocks can be more strongly marked by their lithological characteristics than the Mesozoic formations which here underlie the Creta- |