48 BULLETIN OF THE 



The magnetic variation was observed by Prof. Quimby at 

 Dartmouth College, New Hampshire, throughout the day and 

 evening. The greatest disturbances, reaching 5° of declination, 

 were observed between 12 and 1 o'clock in the afternoon, when 

 the auroral display was at its height in England, while the dis- 

 turbances were far less marked in the evening, when the phenom- 

 enon occupied t!ie entire southern sky at the place of observation. 



Mr. Henry explained that greater deflections might be ex- 

 pected from electric currents on one side of the magnet, than 

 when taking place on both sides, when the fluctuations would only 

 be produced by differences. 



Mr. HiLGARD also read an account of auroral phenomena vis- 

 ible between the observer and the horizon in the background, 

 reported by an observer of the Army Signal Corps in Indiana- 

 polis, confirmatory of similar observations reported by Simpson, 

 Lesley, and others. 



Mr. Powell took the present occasion to report an appear- 

 ance of the same character, witnessed by himself 



Mr. J. W. Powell then made some 



REMARKS ON THE STRUCTURAL GEOLOGY OF THE VALLEY OP THE 

 COLORADO OF THE WEST. 



The lower portion of the Yalley of the Colorado lies but little 

 above the level of the sea, except where short mountain ranges 

 rise- out of the plain. Proceeding up the Valley of the Colorado 

 past the Virgin to a distance of fifty or sixty miles, we find that 

 the country to the north is elevated from fifteen hundred to two 

 thousand five hundred feet above the lower plain. The boundary 

 separating the plain below from the country above, is marked by 

 a line of cliffs stretching across the 'Galley from east to west, in 

 many places vertical for hundreds of feet, and in passing from the 

 plain below to the country above, these so obstruct the way that 

 it becomes necessary to seai'ch for some pass by which the ascent 

 caai be made, and such passes are infrequent. 



His remarks were restricted to that portion of the valley lying 

 between this line of cliffs and the line of the Union Pacific Rail- 

 road. 



This region lies from five to eight thousand feet above the level 



