PETROLOGICAL ABSTRACTS AND REVIEWS 87 
The cycle of activity appears somewhat as follows. In the full 
strength of a volcano’s activity the material ejected is rheumatitic 
and a pedionite is formed. The activity gradually becomes less, and 
aspites, finally tholoides and belonites appear. Sometimes succeed- 
ing the aspite stage there is an alternation of rheumatitic and klasmatitic 
material, and konides are formed, the klasmatitic material forming 
homate cones during the process. Sometimes the intermediate konide 
stage does not appear and aspites are followed directly by homates or 
contain them in the later stages. When the activity decreases still 
further the pneumatolitic stage is reached and the cycle is closed. 
The formation of pedionites, aspites, or konides extends through a 
long period of time, while homates and maares have a brief period of 
development. The explosive process can represent only a single act 
after whose conclusion the activity must be closed forever. Nowhere 
do other forms succeed tholoides or belonites, but pedionites and aspites 
are succeeded by younger forms. Konides always show, in their entire 
cone, the story of the altering forces. They often carry on their extin- 
guished summits the youthful, rapidly built homates, the work of a 
short explosive outbreak. Since the sequence is never reversed, the 
subsequent history of a volcano can be predicted, and the close of a cycle 
is indicated by the form of its last outburst. A volcano cannot be con- 
sidered as active simply because, like Monte Nuovo and El Nuovo, it 
has had an eruption within historic times. From the forms of these 
cones it is seen that they will never again be active. Other volcanoes, 
such as Tambora, Tarawera, and Krafla, which began their activity in 
Tertiary times, are to be considered extinct also, for their last eruptions 
were of klasmatitic material only. This fact is of significance when it 
is applied to such volcanoes as Adatura or Dekeyama in Japan which, 
while it has had no outbreak in 2,100 years, has during all that time given 
off considerable pneumatolitic exhalations. The last outbreaks, how- 
ever, were klasmatitic, and the types are those of the closing cycle. 
The forms, then, of the cones produced, give the key for the deter- 
mination of the stage of a volcano’s history. To say that a volcano, 
which has erupted within the knowledge of man, may again become active, 
or that one which has never within historic times buelsem forth is extinct, 
is to base the assertion upon insecure data. 
Succeeding the discussion of the classification of volcanoes, the author 
gives a chapter on the volcanic formations of central Europe since the 
Tertiary, and considers the geographic distribution of the active volcanoes 
of the present time. The chief volcanoes and volcanic zones are described 
