May 



12, 



I893-] 



SCIENCE. 



255 



feet of drift materials, and the bowlder-strewn region below the 

 valley of Cordoba seems to indicate glacial or iceberg action. 



The interstratification of volcanic and carboniferous rocks 

 seems to indicate that this region has been a centre of volcanic 

 energy for several geological ages, and that the limestones men- 

 tioned occupy a comparatively narrow space along the slopes of a 

 great core of volcanic materials. 



Of the peaks mentioned, Sierra Colorado has an elevation of 

 about 14,000 feet, has a smooth, uniform outline, and the greater 

 portions of its outcropping rocks are of a reddish color. I saw no 

 indications of a crater. Sierra Negra has an elevation of about 

 15,000 feet, with a uniform surface, broken only on the south, 

 where the old crater was situated. The southern or outer wall 

 of the crater has been broken away, leaving the inner or northern 

 wall as an abrupt and rugged section of the otherwise uniform 

 slopes of the mountain (see Fig. 4). The outcropping rocks are 

 dark basalts. 



Seen from a distance, especially when covered with snow, 

 Citlaltepetl seems quite symmetrical, but in winter, or on careful 

 inspection in summer, great ridges of rock may be seen leading 

 up, like giant ribs, from all directions quite to the summit, giv- 

 ing the peak a rugged, restless appearance, so different from the 

 restful outlines of its less elevated neighbors. 



The crater of Citlaltepetl occupies the whole summit. It is 

 somewhat elliptical in form, measuring about 800 feet from north 

 to south by 600 feet from east to west, with a depth of between 

 400 and 500 feet. The rim is nearly horizontal, the difference in 



many evidences of the recent formation of this cone, there is no 

 evidence of an eruption of lava within historic times. 



Between 8,000 and 13,000 feet we saw no rocks, the mountain 

 was covered with a thick mantle of finely pulverized volcanic 

 material, in some cases a black sand, then a sand of lighter color, 

 again it is clay, that frequently appears like rock, called by the 

 Mexicans tepetate. This deposit rises to about the same elevation 

 on Popocatepetl, and to a height of 10,000 feet on the Toluca 

 Mountains west of the City of Mexico, and in some places it con- 

 stitutes the rim of the valley of Mexico. The proposed tunnel 

 for the drainage of the City and valley of Mexico is deing dug 

 through the tepetate, where it is at least 300 feet deep. The 

 material was evidently deposited from water. It seems to indi- 

 cate a more extensive lake system than now exists, and possi- 

 bly more rapid erosion. The presence of this deposit at such 

 high elevations seems to indicate an upheaval of some 3,000 or 4,000 

 feet within comparatively recent times. The geology of this 

 region may not be very complicated, but fossils are not abundant, 

 and there will doubtless be many conflicting opinions among 

 geologists in regard to many of the geological features, yet the 

 geologist who works up the region carefully will find an im- 

 mense amount of very interesting geological material within a 

 very limited area. 



Life on Citlaltepetl. 



With its base in the torrid zone and its summit in the region 

 of perpetual snow, the eastern slope of Citlaltepetl produces 



Fig. 4. — The Peak, seen over Sierra Negra, looking north from Esperanza during the dry 



level between the highest and lowest points being about 80 feet. The 

 peak is a little steeper on the south than on the north, the slope 

 being between 30° and 35° on the south, increasing toward the 

 summit. Inside the crater, for 30 or 40 feet, the slope is about the 

 same as outside, then about 200 feet of vertical walls, then a 

 sharp talus to the centre, as shown in the annexed cross-section. 



The hot sunshine by day and the intense cold at night, with 

 plenty of moisture during a large part of the year, result in rapid 

 disintegration of the crater walls, cutting down the rim, and 

 filling up at the bottom with fragments from the crumbling walls, 

 so that, geologically speaking, the crater can exist but a short 

 time. The ruggedness of the slopes and the fact of a crater seem 

 to indicate that the peak is of recent formation. Citlaltepetl has 

 a hot top, at least great areas of the rim of the crater are hot, 

 giving off steam and gases, and large quantities of rocky material 

 at the summit are the product of this fumarole action. Sulphur 

 is found in considerable quantities in the rim of the crater, but I 

 saw no evidence of sulphur gases, or anything to indicate that 

 sulphur is being deposited at the present time. While there are 



almost every variety of vegetable and animal life. From the 

 coast up to the 1,500 feet level, the country is practically a 

 steppe; rainfall limited, soil sterile, vegetation scanty except 

 along the streams; birds, insects, lizards, etc., abundant with 

 but few mammals. 



The region between 1,500 and 6,000 feet is the life-centre of 

 this slope, the rainfall is abundant, and the soil, composed of the 

 debris of volcanic and limestone rocks, is exceptionally fertile, 

 producing a vegetation of great variety and luxuriance. The 

 forest trees are seldom large but they exist in great variety, bear- 

 ing ferns, orchids, bromelias, and other plants in great profusion 

 on their trunks and branches ; and every spot not shaded by the 

 forest is crowded with a rank growth of herbaceous plants. 



While in Cordoba, at an elevation of about 3,000 feet, I met a 

 man from New York, who was buying Mexican lumber for the 

 inside finish of his house, and went with him out to a little saw- 

 mill, where there was not more than 2,000 feet of lumber in stock. 

 From this small quantity 65 pieces were selected, and, on count- 

 ing, the man found he had 41 different kinds, all valuable as fin- 

 ishing lumber. It is said that there are as many as 100 different 

 kinds of trees on the slopes of Orizaba that are valuable for 

 lumber, besides many that furnish valuable dyes, oils, or gums. 



This region is also famous for its orchids and ferns. I saw in 

 Cordoba a collection of 70 species of native orchids, and was told 

 that the collection did not contain nearly all the species of the 

 region. Mr. Hugo Finck has sent to the K.ew gardens from this 



