POPOCATEPETL AND IXTACCIHUATL—FARRINGTON. 1 
extent and number of these lakes, of which such modern ones as 
Texcoco and Chalco are but shrunken remnants, is shown by lacus- 
trine deposits found on the slopes of the mountains, and by plains, 
such as the plain of Ameca, which were once lake beds but are 
now dry. 
In the view of Packard there was also a glaciation of the entire 
region, presumably at the time of the Glacial Period, but of this 
extensive glaciation I was myself unable to find further evidence. 
ROUTE TO THE MOUNTAINS. 
The starting point usually chosen from which to make an ascent 
of either of the two principal peaks of the Sierra is Amecameca 
Or, as it is commonly known at the present time, Ameca. It is a city 
of about 12,000 inhabitants, situated nearly forty miles by rail south- 
east of the City of Mexico. 
It is reached by the Morelos division of the Inter-oceanic Railway, 
the ride from the City of Mexico occupying about two hours. The road 
passes out first over the level expanse of a plain formerly included in 
Lake Texcoco, the water of which may be seen to.the east. A few 
miles further on the cones of a number of extinct craters can be seen 
on either side of the way. These belong to the range of the Santa 
Catarina volcanoes on the west, while the cone of El Pino lies to the 
east. These are all minor eruptive cones of comparatively recent 
formation, and consist, together with brecciated and scoriaceous 
materials, chiefly of hypersthene-andesite, a rock corresponding to 
that of the later flows of Popocatepetl. 
The road then skirts the shore of Lake Chalco, the extent of 
water in which varies greatly with “the ‘season. From: here. the 
ascent is rapid, the road winding about in huge curves, to gain the 
higher plain of Ameca. To the east rises the peak of Tenayotl, 
a hill of hypersthene-andesite, its slopes clothed with forests of 
pine. Behind it stands the snow-crowned Sierra. To the west 
are the craters and cones of the group of volcanoes of which Ajusco 
is chief—a barren and desolate range. The slopes of many of these 
cones are unusually steep and their shape typically volcanic. The 
rock of which they are composed is basalt, so that volcanoes closely 
associated in time and space poured forth the one an acidic, the other 
a basic lava. 
