830 HENRY S. WASHINGTON 



with its great crater lake, which will form the subject of the 

 next paper. 



It may also be noted that volcanic activity seems not yet 

 entirely extinguished, since several hot springs occur in the 

 neighborhood. The best known of these is that of Bulicame, 

 which lies about 2''™ to the west of Viterbo. This was probably 

 known to the Romans, is mentioned by Dante, and is still flow- 

 ing abundantly. The temperature of the water is 80°.^ Verri 

 also notes a few others near Ronciglione and Orte, and calls 

 attention to the great deposits of travertine as evidence of the 

 former abundance of mineral springs in the region. 



We see from the above sketch that the structure of the region 

 is somewhat different from that of the Bolsena region, since we 

 find external to the great crater ring, and older than it, the 

 Monti Cimini, and inside it the younger dome of Monte Venere. 



A much more thorough study than has yet been attempted 

 must be devoted to the region before all the problems it pre- 

 sents can be solved, but mention may here be made of the chief 

 theories which have been proposed to account for some of its 

 features. Since Verri's paper is the most detailed that we pos- 

 sess on the region it will not be out of place to quote briefly 

 from his own resume- of his views on the geological history 

 and structure of the volcano. 



According to him eruptions of fragmentary material broke 

 out toward the close of the Pliocene period, and resulted in 

 forming an island of trachytic tuff in the midst of the shallow 

 sea. This was followed by eruptions of more solid material 

 which formed Monte Cimino in the center of the island. After 

 retreat of the sea consequent upon upheaval of the surface, 

 which fractured the dome, trachytic lavas were poured out of 

 the fissures thus made. 



After this there was opened the Vico vent, both vents 

 erupting simultaneously at first, though the eruptions of Monte 

 Cimino soon ceased. With the opening of the Vico vent there 



^Daubeny, Volcanos. London, 1848, 160. 

 ^ Verri, op. cit., 33. 



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