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 inter- 

 ruptions 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 ex- 

 posures of the Plateau Province, and their features are as characteristic 

 of the formation as the peculiarities of the Trias; but the wonderful per- 

 sistence 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- 



