244 HENRY S. WASHINGTON 



the leucitites, and covering almost all the western part of the 

 cone, are leucite-tephrites, whose amount, while great, is not 

 equal to that of the leucitite. These also appear as small flows 

 in the northern and eastern parts. Belonging to th'is period are 

 certain tuffs, the most extensive of these being a gray lithoidal 

 tuff which covers the flanks and extends for a great distance to 

 the north, east, and south of the volcano. Moderni estimates 

 that the volcano at the close of this period had an altitude of 

 nearly 3000 meters. 



The second or trachytic phase was inaugurated by the blow- 

 ing out of the large central cavity, which involved the destruc- 

 tion of the greater part of the northern and eastern wall. It 

 was during the first part of this phase that the double dome of 

 Mti. Sta. Croce and Lattani was formed. These form, as already 

 observed, a homogeneous compact mass, and are a good example 

 of a "domal" eruption of a pasty magma which was not suf- 

 ficiently fluid to flow to any great distance. The material of 

 this eruption was of a trachy-andesite approaching the vulsinites 

 already described, while the other eruptions of this period were 

 of a more acid and more nearly trachytic rock and were all flank 

 eruptions. While stating that it is impossible to decide definitely 

 whether the central domal or the flank eruption took place first, 

 Moderni thinks it more probable that the former was the earlier. 

 He bases this conclusion on the ground that the large domal 

 eruption choked up the main central vent, so that any further 

 ejection of volcanic material had to take place through the flanks 

 of the volcano. It is needless to mention in detail the various 

 trachytic flows, which moreover are not nearly as large in amount 

 as the flows of the first phase. With the trachyte there was also 

 erupted a small quantity of leucitic rock. Several areas of tra- 

 chytic tuffs also belong to this phase. 



The third and last phase of activity was characterized by the 

 eruption of basaltic rocks in which leucite is entirely wanting. 

 These eruptions were of small amount, the quantity of basalt 

 being even less than that of the trachytes. They formed a num- 

 ber of small parasitic cones, the lava poured out being often 



