Geology and Mineralogy. 157 



in the Monthly Weather Review, or any similar publication, are 

 arranged in periods of twenty-seven days, six hours, and forty 

 minutes, so that corresponding days of the successive periods fall 

 in the same vertical columns, it will be found that the larger 

 numbers showing increased prevalence of the aurora are grouped 

 together as a rule, indicating the existence of a periodicity 

 at this interval, which corresponds to the most generally ac- 

 cepted value for a synodic revolution of the sun. The succes- 

 sion of larger numbers in the same vertical columns is generally 

 interrupted near full moon, seemingly because of moonlight, so 

 that the track of the moon can be traced, extending diagonally 

 across tables constructed in this way. Aside from these breaks 

 the periodicity is at times clearly apparent for years in succession. 

 The six hours, or one-quarter day, may be provided for by adding 

 a day to each fourth period, and the forty minutes or one thirty- 

 sixth of a day by adding a day to each thirty-sixth period. 



Lyons, N. T., Jan. 16, 1891. 



II. Geology and Mineralogy. 



1. Ninth Annual Report of the United States Geological Sur- 

 vey to the Secretary of the Interior, 1887-'88, by J. W. Powell, 

 Director. Washington, 1889. The opening pages (1-44) of this 

 volume give the Report of the Director, indicating the progress 

 made during the year in the various departments ; this is followed 

 (49-154) by administrative reports by the heads of divisions. 

 The bulk of the volume is given to four long and valuable papers: 

 (1) pp. 209-528 by Capt. Dutton on the Charleston Earthquake 

 of Aug. 31, 1886 ; (2) pp. 537-610 by Prof. Shaleron the geology 

 of Cape Ann, Mass.; (3) pp. 619-676 by W. H. Weed, on the 

 formation of travertine and siliceous sinter by the vegetation of 

 hot springs (specially noticed below) ; (4) by Dr. C. A. White on 

 the geology and physiography of a portion of northwestern Colo- 

 rado and adjacent parts of Utah and Wyoming. The discussion 

 of the Charleston earthquake by Capt. Dutton is exhaustive and 

 able, and the results of much value. The earthquake is remark- 

 able as one of great severity, taking place independently of any 

 region of volcanic activity. The conditions existiug for obtain- 

 ing a full record, over the country involved, of the time, duration 

 and effects of the earthquake were on the whole unusually favora- 

 ble, and the energetic action of several gentlemen connected with 

 Survey, aided by Mr. Earle Sloan and others of Charleston, has 

 resulted in the accumulation of a large amount of material, em- 

 bracing no loss than 4,000 reports from 1,600 localities. The de- 

 tailed descriptions of the phenomena observed are supplemented 

 by independent and o-raphic accounts by three observers in 

 Charleston, Messrs. McKinley and Fisher, and Dr. Manigault. A 

 large number of full page illustrations from photographs give a 

 striking impression of the damage done. 



