16 MESOZOIC FLORAS OF UNITED STATES. 



The absence of plant impressions enabled me to devote more attention 

 to geological considerations than would have been practicable had large 

 collections of plants been made; and I regard the geological results as of 

 sufficient importance to be introduced here somewhat fully. This chapter 

 will therefore be divided into two parts, the first of which will deal with 

 the stratigraphy and the second with the paleontology. 



STRATIGRAPHICAL RELATIONS OF THE OLDER MESOZOIC DEPOSITS OF 



ARIZONA. 



The geology of the Grand Canyon region of northern Arizona has 

 received much attention on the part of geologists, and considerable has 

 been written on the higher beds of Mesozeic age that lie to the eastward 

 and northward, but very little study seems to have been made of the 

 Little Colorado Valley above Coconino Point, where it broadens out into 

 a plain. The strata of the Grand Canyon up to and including the junction 

 of the Little Colorado with the Colorado River consist, as all know, 

 entirely of Paleozoic and pre-Paleozoic rocks, and it is the Carboniferous 

 limestones, or sometimes sandstones (LTpper Aubrey), that occupy the 

 surface of both the Colorado and the Kaibab plateaus. But the entire 

 system dips sensibly to the northeast, and at an}^ point some distance 

 back from the camion remnants of Mesozoic rocks occur for many miles 

 to the west of the Little Colorado. That river, therefore, practical^ flows 

 for almost its entire length over Mesozoic strata, iDut these do not attain 

 their great development except on the northeastern slope of the valley. 

 Here they form several series of terraces, rising one above another l^ack- 

 ward from the river, and forming at their m.aximum development loft}' 

 and picturesque escarpments, with brilliantly colored stratification, rival- 

 ing in many respects the Grand Canyon itself. The broad, arid plains 

 that lie to the southwest of these cliffs have received the name Painted 

 Desert, from the circumstance that from any point on this desert these 

 "painted" cliffs are always in full view. From a great distance they 

 may under certain conditions appear beautiful and innocent, but any 

 attempt to invade this desert or to scale these cliffs, except by means of 

 the few well-known Lidian trails, is certain to be met with defeat, and the 

 hardships that have to be endured in striving to traverse this region are 

 of the severest kind. 



