254 



SCIENCE. 



[Vol. XXI. No. 536 



be about^the average level of the snow-line. As the dry season 

 comes on, the snowfall gradually ceases, and the snow that has 

 accumulated during the summer rapidly disappears under the 

 heat of a tropical sun ; rocky ridges and loose sands appear on 

 the south and east, while an extensive'glacier is disclosed on the 

 north and west. (See Figs. 1 and 5 for^summer views and 3 and 

 4 for winter views.) The glacier on the southwest extends down- 

 ward to about 16,350 feet, narrow tongues of ice reaching 400 or 

 500 feet further downward, while on the north the main body 

 descends nearly to 15,000 feet. In April, 1892, near the close of 



.—The Peak from the 13,000 ft. level 

 Colorado on the left. 



the southwest. Sierra 



the dry season, the snow had disappeared and the ice had re- 

 treated some distance, leaving a valley or series of basins between 

 the glacier and the crest of the moraine. In these basins were 

 streams and ponds of water, small bodies of ice and broken rocks. 

 (See Fig. 2 and Fig. 3.) The moraine is from 100 to 300 feet high 

 on its outer face, and from nothing to 15 feet on its inner slope. 

 Tbe moraine is as steep as loose rocks will stand, but the rocks 

 composing it are by no means loose, they are bound together 

 with ice. The ice is continually melting from the outer face of 

 the moraine, but the mass is practically constant, apparently 

 supplied by water from the melting glacier above. Water from 

 the glacier sinks slowly into the moraine, becoming ice again, 

 later it melts from the face of the moraine and is absorbed by 

 the rocks and sands below, without forming streams. I only saw 

 one instance of a stream across the moraine, and it soon disap- 

 peared in the porous rocks. Dry drainage channels indicate that 

 sometimes there is water enough to form streams, but, in general, 

 there are no streams above 12,000 feet, and those below are few 

 and small, on account of scanty rainfall and porous rocks. While 

 it snows frequently during the summer, the total amount does 

 not seem to be very great. The slope on the north is more gradual, 

 so that the glacier on the north, measured along the slope, is 

 about five miles long, while on the west it is not more than two 

 miles in length (see Fig. 6). The width is from eight to ten 

 miles, and the thickness or depth from 10 feet to 50 feet, I 

 found no polished bowlders or striated rocks, the only evidences 

 of motion were occasional crevasses, and the interval between the 

 moraine and the ice. During the summer the glacier probably 

 advances to the moraine, and both are generally covered with 

 snow, but, on a photograph of the peak (Fig 1), taken from an 

 elevation of about 13,700 feet, Aug. 3, 1891, after eight days 

 without snow, the moraine can be seen as a sort of terrace across 

 the slope of the mountain, while on July 38 and 29 it was entirely 

 hidden by snow. The fact of the glacier on the west and north 

 seems to indicate that more snow falls on those slopes, and that 

 the moisture from which it is formed comes from the west. But 

 the moisture might come from the Gulf, and the snow formed on 

 the east be carried to the western slopes by the wind. From the 

 storms I saw, I judged that the snow was somewhao equally dis- 

 tributed over the mountain, whether the storm was westerly or 

 easterly, and that the glacier on the north, and the naked rocks 

 and sands on the south, were due to the fact that more snow 



melted on the south, rather than that more snow fell on tbe 

 north. 



At first I felt sure that the glacier had its source in the Pacific 

 Ocean, but the more I investigated the matter the more I inclined 

 to the view that much of it might have come from the Gulf. 

 These glaciers are not very extensive as glaciers go, but they 

 present many interesting features for study, and they are easily 

 accessible, one can ride to the foot of the moraine with little 

 danger or fatigue. And there is little or no danger attending tbe 

 exploration of the glacier, beyond the physiological effects of the 

 great elevation. From January to the middle of April the glacier 

 may be seen at its best. No danger from snow-slides or ava- 

 lanches, and crevasses are not numerous or extensive, and can be 

 easily avoided. In summer, there are occasional snow-slides on 

 the western slope, and after 10 a.m. on a clear day there might 

 be some danger from snow-covered crevasses, but earlier the 

 frozen snow forms a safe bridge over any crevasse there may be 

 in the glaciers of the Star Mountain. 



Ice is quarried from the glacier for domestic use in the sur- 

 rounding towns. The ice is taken out and dragged to the foot 

 of the moraine and there loaded on burros or horses for transpor- 

 tation to the lower slopes. 



Geology. 



Citlaltepetl, Sierra Negra, and Sierra Colorado are the culmi- 

 nating domes of a great mass of volcanic rocks, wbich forms part 

 of the eastern boundary of tbe famous valley of fflexico. This 

 mass, about 50 miles in diameter, at the 8,000 feet level, rises by 

 gentle slopes to the 13,000 feet level, above which i-ise the peaks 

 mentioned. Citlaltepetl, the highest, is somewhat cone-shaped, 

 but Sierra Colorado and Sierra Negra are ridges trending east and 

 west, each about a mile in length. Sierra Negra is about five 

 miles, a little west of south, from Citlaltepetl, and Sierra Colorado 

 is about three miles southwest of the same peak. 



From the summit of these peaks down to tbe 8,000 feet level 

 trachytes, basalts, and scoriaceous rocks seem to make up the 

 bulk of the mass. Then there are 200 or 300 feet of Cretaceous 

 limestone in nearly horizontal strata, then from 800 to 1,000 feet 

 of Jurassic limestone, whose crumpled and folded strata remind 

 one of the folded rocks of Arkansas, thence down to about 4,000 

 feet there are several alternations of basaltic rocks and Carbonif- 



PiG. 8.— Detail at the foot of the glacier seen in Fig. 2. 



erous limestones. Near the city of Orizaba the limestone is 

 thick-bedded and associated with beds of quite good marble and 

 beds of the famous Mexican onyx. Below the city there are De- 

 vonian limestones, then Carboniferous strata to about 2,500 feet, 

 then Cretaceous to the coast sands, about 35 miles from the Gulf. 

 I noticed the succession of rocks, but did not attempt to identify 

 the limestones, I name them as identified by Mr. Hugo Finck of 

 Cordoba. 



According to Mr. Finck, the different phazes of the Glacial, 

 Champlain, and Terrace periods are well marked in this portion of 

 Mexico. The valleys of Orizaba and Cordoba were occupied by 

 glacial lakes, over whose beds were deposited several hundred 



