ITALIAN PETROLOGICAL SKETCHES 83 I 



appears a new mineral, leucite, which increases in abundance till 

 toward the close it predominates largely over the other con- 

 stituents. The eruptions of leucitic lavas were followed by 

 those of lapilli, terminated by an explosion which threw out of 

 the cone torrents of mud.burying the surrounding country for a 

 distance of ten to fourteen kilometers. 



The internal equilibrium of the cone was disturbed by the 

 eruption of this vast amount of fragmentary material, and the 

 greater part of the cone sank in, Monte Venere alone remaining 

 above the waters of the lake — a fragment of the former sum- 

 mit which the action of the weather has reduced to a cone- 

 shaped figure. 



There are grave objections to be brought against certain 

 points of this sketch, and Deecke devotes considerable space to 

 arguments against two of them. He holds that Monte Cimino 

 was not the result of a"domal" eruption of pasty trachytic 

 magma followed by lava streams, as vom Rath and Verri believe, 

 but that the mountain is part of what remains of the large 

 crater ring of a true strato- volcano. The northwest wall of this 

 has entirely disappe^ared . and of the original cone, only Monti 

 Cimino, Valentano^ La Pallanzana and one or two others are 

 left. The crater was filled up, partly by its own eruptions and 

 partly by the ejections from the neighboring Vico crater. 



He agrees with Verri in thinking that the latest eruptions 

 from the Cimino crater took place after those of Monte Vico had 

 begun; but regards them as composed of "petrisco," which he 

 considers with vom Rath to be a trachyte enclosing many leucites 

 derived from the Vico lavas. 



The arguments which he brings up against Verri's views that 

 the crater lake of Vico is due to a sinking in of the top of the 

 cone, and that Monte Venere is a half-sunken fragment, seem to 

 me to be quite conclusive. They are so well given in his easily 

 accessible paper that the reader is referred to it for a full pres- 

 entation of them. He considers the crater a double one, due 

 to jwwerful explosions, perhaps aided somewhat by sinking, 

 and Monte Venere a true dome ox puy — the last eruption of the 



