REVIEWS. 
Expedicion Cientifica al Popocatapetl. Josk G. AGUILERA Y EZE- 
QUIEL ORDONEZ. Mexico, 1895. 8vo, 48 pp., 6 plates and 
2 charts. Published by the Geological Commission of 
Mexico. 
THE volcano, to a description of which this pamphlet is devoted, 
is perhaps the most widely known of any in the Western Hemisphere. 
From the time of Cortez to the present, its towering height and con- 
dition of semi-activity have made it a subject of continual interest. 
Yet the descriptions of it so far published have, from a scientific point 
of view, been meager and fragmentary. Humboldt in his work on 
Mexico makes but brief mention of it. Later travelers, notably Felix 
and Lenk, have added much to our knowledge of the mountain, but 
their accounts have failed to give sufficient data to permit intelligent 
comparison of its characters with those of other great volcanoes. 
It is, therefore, a real service to the science of geology which the 
authors of this pamphlet have done, in preparing so comprehensive 
and careful a description of the features of Popocatapetl. While full 
recognition is made of the work of previous observers, the larger part 
of the data are original with the authors themselves. So compre- 
hensive, moreover, is the treatment of the subject that future study of 
the volcano may profitably be confined to special portions or phases of 
its structure. 
The work begins with a description of the orographic relations of 
the volcano, it being shown that it forms the most southern and high- 
est part of the Sierra which separates the valley of Mexico from the 
valley of Puebla. The form of the volcano is stated to be that of an 
elliptical cone whose major axis has a northwest-southeast direction. 
The cone is formed of three parts, the upper, covered by a mantle of 
perpetual snow, and hence having a uniform slope, the median, com- 
posed of sands whose surface is cut by radiating channels made by the 
flow of waters from above, and the lower, which is part of the highly 
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