80 APPENDIX TO EEPORT OF THE SECRETARY. 



beds. This may carry the period of faulting far into the miocene period, 

 or possibly as far as the commencemeut of the pliocene. But while the 

 first stage in the activity of these ancient volcanoes was undoubtedly 

 the greatest, and accompanied by an incomparably greater amount of 

 extravasation, it by no means constitutes the whole of it. Even after 

 the great displacements, and after the principal topographic features of 

 the country, depending upon structure as they now exist, had received 

 their shape, minor eruptions continued ; they present, however, a some- 

 what remarkable fact. The later eruptions did not take place froni the 

 same centers as the earlier ones, but show a tendency to recede from 

 them and to occur around the borders of the older volcanic district. 

 The central portions of the volcanic area are unquestionably the oldest, 

 while the younger ones are found around their borders, and sometimes 

 at considerable distances. 



One point which during the study of this region: has engaged the care- 

 ful attention of Captain Button has been to ascertain whether it presents 

 any such sequence in the lithological character of the eruptions as is 

 asserted by Baron Kichthofen to prevail in the volcanic districts of 

 Europe, South America, Asia Minor, and the Sierra Nevada. This as- 

 serted sequence has engaged the profound attention of most vulcauolo- 

 gists and is of great importance in relation to all questions bearing upon 

 the origin and causes of volcanic action. Although at first disposed to 

 doubt the prevalence of this sequence, and not favorably impressed with 

 the speculations and theoretical views of Baron Kichthofen, Captain 

 Button has reached the conclusion that the high plateaus of Utah ex- 

 hibit in a decided manner essentially the same sequence which Kicht- 

 hofen claims for other volcanic regions. The earliest eruptions consist 

 of rocks agreeing well in lithological characteristics with those described 

 by Kichthofen under the name of propylite. This rock is usually con- 

 cealed if it exists in any great quantities by the later flows, but is in 

 several places brought to light partly by the great displacements, and 

 partly through the agency of erosion, and wherever found it is seen to 

 occupy the lowest position of all. It is also worthy of note that this 

 rock is found at those points which constitute the centers of eruption 

 before referred to, showing that the activity which it ushered in con- 

 tinued to have its seat through a long cycle in and about the same lo- 

 cality. The propylite is succeeded by a rock answering to Kichthofen's 

 description of hornblende andesite, which is usually overlaid by a rock 

 rich in augite with triclinic feldspar which may be termed augitic ande- 

 site. Still higher in the series are found immense masses of trachyte 

 which, however, is frequently intercalated with dolerite. The variety of 

 the trachytes is very great ; so great, indeed, that were it not for the per- 

 sistence of certain mineralogical as well as textural characteristics which 

 are universally accepted as being distinctive of that group of rocks, one 

 might feel strongly tempted to make numerous subdivisions of them into 

 a series of groups. The extremes of the varieties of the trachytes 



