108 E. L. Berthoud—McClellan Mountain, Colorado. 



as the sectional area of the magn't. The 

 ,- of where the hole through the center is 



I advantage, is that of tbe deflecting magnets for determining 

 tbe intensity of the earth's magnetism, which may be thus 

 made lighter withoat much diminishing their magnetic moment. 



In conclusion, let me express my regret at the imperfection 

 of the theory given in this paper; for although the equations 

 are more general than any yet given, yet still the}/ rest upon 

 two quite incorrect hypotheses; and so, although we have 

 found these formulas of great use in pursuing our studies on 

 magnetic distribution, yet much remains to be done. A nearer 

 approximation to the true distribution could readily be obtained, 

 but tbe results would, without doubt, be very complicated and 

 would not repay us for the trouble. 



In this paper, as well as in all the others which I have pub- 

 lished on magnetic subjects, my object has been not only to 

 bring forth new results, but also to illustrate Faraday's method 

 of lines of magnetic force and to show how readily calculations 

 may be made on this system. For this reason many points 

 have been developed at. greater length than would otherwise 

 be desirable. 



Art. IX.— On rifts of L-e in the rocks near the summit of M 

 McCiellan, Colorado] and on the different Limits of Vegetation on 

 adjoining summits in the Territory; hy Edward L. BeethoUD- 



The silver mines of Argentine District, a mining center about 

 eight miles southwest from Georgetown, are located on the north 

 slope of a high peak named McCiellan Mountain, which forms 

 a very prominent point of the main central range, and immedi- 

 ately facing a precipice fully 1500 feet high, the majestic 

 mass of G-ray's Peak ; while l"^ miles south is Argentine Pass, 

 13,100 feet in height. 



This mountain, 13,430 feet* above the sea, is intereected in a 

 northeast and southwest direction by a system of mineral veins, 

 containing silver in large quantity with a little gold. The veins 

 seem generally to be nearly vertical, and occur at elevations 

 varying from 12,300 feet to 13,400 feet. Three of them have 

 been extensively mined, and two, the International and Belmont, 

 have been developed and worked since 1867-68 with success, 

 and with fair paying results; but with probably at a greater 

 average cost per ton of mineral mined than any "other similar 

 mines in Northern Colorado. The Centennial Lode, the third 

 mine examined, is now being well developed by its owners, who 

 * Vide Gardner, in Hayden'a Report, 1873-14 



