1892.] Geology and Paleontology. 843 
tance between the two localities is considerable and the atmospheric 
conditions are usually very diverse, yet the results are very close to 
those of Dr. Franz Kaska who used two mercurial barometers, of 
mountain form, read at about the same time, one on the summit of the 
mountain and one at Chalchicomula about twenty miles away. The 
elevation of the datum point in Chalchicomula was determined by 
railway levels. 
From the datum point used by Dr. Kaska, assisted by Mr. O. G. 
Bunsen I carried a line of spirit levels up to the 14,000 feet level. 
Higher it did not seem practicable to go, on account of snow, steep 
slopes, high winds, etc. From that elevation we made two ascents, 
one on July 29, 1891, and one on August 3, 1891. I used an aneroid 
barometer adjusted by comparison with a standard mercurial barom- 
eter. On each ascent the barometer was read at the summit about 2 
o'clock P. M., and at the 14,000 feet level at about 5 o'clock P. M. 
The readings for July 29, reduced by the method of the U. S. Coast 
Survey, indicated a difference in elevation between the 14,000 feet 
level and the summit of 4139.20 feet, while those of August 3 by the 
same method indicated a difference of 4219.12 feet. The average of 
these results 4179.16 feet plus 14,000 feet gives a total elevation of 
18,179.16 feet, a result surprisingly near that of Prof. Heilprin. Prof. 
Heilprin estimated that his station was 120 feet below the summit. 
My aneroid barometer indicated that it was only eighty-six feet below 
the true summit; subtracting this difference of thirty-four feet from 
Prof. Heilprin’s figures, and the two results 18,171 feet and 18,179 
feet differ by only 8 feet. 
The atmospheric conditions on July 29 and August 3, to the senses 
seemed identical, yet the difference as shown by the barometer was 
considerable, and the barometer, when checked with the spirit level 
elevations, gave varying results. These variations, while not wide, 
gave rise to a feeling of uncertainty as to the trustworthiness of the 
barometer in determining such high elevations. 
In April 1892, assisted by Sefior E. O. Moreno, I measured a base 
line 1550 feet long, near the 13,000 feet level and obtained the angles 
necessary to determine the elevation of the peak above each end of 
the base line, a large cross planted on the summit forming a definite 
point of observation. The results show an elevation of 18314.357 feet, 
as follows : 
