Y OF 



PREFACE. 



The region of country embraced in the map which accompanies this 

 report is one of great geological interest. Three great categories of facts 

 are here represented on a grand scale, viz: facts relating to displacement, 

 facts relating to degradation, and facts relating to sedimentation. The dis- 

 placements arc of great magnitude, and because the beds involved are sedi- 

 mentary strata but rarely altered, the characteristics of these displacements 

 are plainly revealed, so that in our studies of them we have been able to 

 arrive at conclusions, both quantitative and qualitative, with some degree of 

 certainty. 



While displacement has been great, degradation has also been great, 

 yet the country has not been planed down to a general base-level, but stands 

 in mountain cliffs and escarped hills, where the strata are plainly revealed.. 



The formations which we are able to study here have an aggregate 

 thickness of 50,000 feet, and embrace groups of Paleozoic, Mesozoic, and 

 Cenozoic Ages. Throughout nearly the entire region there is a condition of 

 surface which renders the study of the geology comparatively easy. By 

 reason of great altitude and extreme aridity the rocks are rarely masked by 

 subaerial gravels, soil, or vegetation, and the book of geology lies open. 

 We have thus been able to collect a large body of facts, which, in the fol- 

 lowing volume, have been arranged in such order as it seemed would best 

 present to the reader the general geology of the country. Many details 

 have been omitted which would have been given had the facts been pre- 

 sented as they w*ere collected in the form of an itinerary, but it was though 

 that, such a method would result in encumbering geological literature with 



a mass of undigested facts of little value. 



Ill 



