XXli GEOLOGY OF THE HIGH PLATEAUS. 



lavas and the conglomerates would obviously be impossible. With the 

 foregoing exceptions the distribution of the strata is given with great con- 

 fidence In the exceptional cases the errors are believed to be so small as 

 not to sensibly impair the accuracy of the map. 



The relief map was prepared in the following manner : A plaster cast 

 about five feet square was made, the horizontal and vertical scale being the 

 same. The data for the cast were obtained from the contour map. The 

 cast was then photographed, and a copy of the photograph was drawn upon 

 stone. 



The map (Sheet No. 4), showing the arrangement of the faults and 

 flexures, was designed to show at a glance the connection, relations, and in 

 some cases the continuity of the greater structure lines of the High Plateaus 

 with those of the Kaibab district around the Grand Canon of the Colorado. 

 The Kaibab or Grand Canon faults have been already worked out in an 

 admirable manner by Powell. The importance of connecting the two dis- 

 tricts by these common features is very great, and is not only essential to 

 the present work, but will have, if possible, still greater importance when 

 the geology of the southwestern part of the Plateau Province is discussed. 

 Only the greater displacements are here given. There are very many 

 smaller ones which are not so well known nor so well identified. Those 

 which are given have been traced rigorously mile by mile so far as they 

 are represented, excepting, however, the portions which extend south of the 

 Colorado. The course of these faults south of the Grand Cation has been 

 given to me by Mr. G K. Gilbert, who has in part identified their existence 

 in that region, though I presume that he would not wish to be understood 

 as attaching a veiy high degree of accuracy to his designations, having 

 made merely a preliminary reconnaissance in that region. 



The stereogram has been worked out with £ - reat care. It. is the con- 

 solidated expression of a very large number of sections made in the field, 

 together with the results obtained by tracing continuously each fault along 

 its course This mode of illustrating displacements is by no means all that 

 could be desired and lias some serious defects But it seems to be a great 

 improvement in the means of illustrating structure, since it groups the 

 dominant features together in their proper relations. Probably the greatest 



