p. Waitz— Popocatepetl Again in Activity. 83 



main cone is especially thick on this side and a very 

 special kind of stratification diminishes the velocity of 

 propagation of the heat waves from the depth toward 

 the surface. The glacier reaches from the main summit, 

 the Pico Mayor of the volcano (5450 m.), on the north- 

 west slope of the cone, down to about 4800 m. We also 

 found on the north side of the cone the side which was 

 used for the ascent, small patches of snow in the depres- 

 sions where it had been accumulated by the wind. On 

 the east, south and west slopes the cone was entirely free 

 from snow. 



I arrived at the lowest part of the crater rim at 9 : 30 

 A. M. During the interval before my friends could join 

 me I was able to study the crater and observe a rather 

 strong eruption. At 11 o'clock we began to ascend on the 

 rim of the crater, climbing along its east and south side 

 in order to reach the highest point lying on the west side, 

 where we arrived at 2 p. m. We climbed down on the 

 other side of the crater rim until we again reached its 

 lowest portion and from there went quickly down to Las 

 Cruces and Tlamacas. Here we remained a second night 

 and after having been able to observe and photograph a 

 very strong eruption at 7 o'clock, the next morning we 

 rode to Amecameca, and returned to Mexico City, where 

 we arrived on the evening of the same day. 



With the exception of the disappearance of the snow 

 cover, the form of the mountain has not changed since 

 the beginning of its new stage of activity. The crater 

 also has preserved its form and figure, at least no consid- 

 erable changes could be observed, and comparing the 

 pictures of the crater which I made in 1905 with those 

 taken on the present trip, I cannot find any changes. This 

 does not apply, however, to the bottom of the crater. 

 As long ago as 1895, Aguilera and Ordonez, who at that 

 time studied the mountain and measured the crater, 

 remaining at its bottom for several days, described in its 

 lowest portion a small lagoon, which was also well known 

 to all those who had ascended Popocatepetl during the 

 last 20 or 30 years. This lagoon has disappeared and in 

 its place, but of much greater dimensions, I found an 

 elliptical accumulation of andesite bowlders. This hill 

 has a NW-SE longitudinal axis about 100 m. long, a 

 transverse axis about 75 m. wide, and a height of 40 to 

 50 m. There is no doubt that this hill of black andesite 

 bowlders is the upper part of a lava plug which after the 



