Geology. 401 



over the destroyed area, which now largely conceals the traces of 

 the great catastrophe. Already the streets of Saint-Pierre are 

 being cleared out and are beginning to be rebuilt by the new 

 population settling there. 



The writer discusses the structure of the dome of Pelee and, 

 after comparison of the texture of its rocks with those of Amer- 

 ican laccoliths, is led to the conclusion that the effect of pressure 

 in determining the micro-granular texture of quartzose igneous 

 rocks is much less than has been generally supposed. 



In the third chapter different types of volcanic eruption are 

 considered ; the author makes four classes : a, the Hawaiian, in 

 which the lavas are extremely fluid and the vapors escape with- 

 out causing projection of solid material ; b, the Strombolian, in 

 which the lava is more viscous and the escape of vapors takes place 

 with explosive activity with the projection of some pasty mate- 

 rial which falls as rounded, flattened bombs ; c, the \ r ulcanoan, 

 in which the lava solidities at the surface between eruptions, and 

 this, and the very viscous condition it is in, causes the explosions 

 and escape of the gases to be accompanied by quantities of 

 broken solidified rock, which falls as angular bombs, lapilli, etc.; 

 d, the Peleean, whose explosion occurs in material already solidi- 

 fied, giving rise to incandescent clouds composed of an intimate 

 mixture of gas and solid material whose weight is so great that 

 they roll rapidly down the mountain side, if not contained more 

 or less in a caklera of sufficient size, producing the direful effects 

 seen at Saint Pierre. It will be noticed that this classification is 

 a progressive one depending on the proportions of gas and solid 

 material and on the relative condition, liquid or solid, of the 

 magma. It could be reduced to two, the Strombolian, of which 

 the Hawaiian is an extreme case in one direction, and the Vul- 

 canoan, of which the Peleean is an extreme case in the other. These 

 definitions, which are essentially those employed by the Italian 

 geologists, are more precise than the "quiet" and "eruptive" 

 types of the geological text-books. 



The author calls attention to the fact that many volcanoes vary 

 between these tyj)es according to the character of their magma, 

 but that such variation may take place in the history of a single 

 volcano and even in a single eruption. 



In the final portion of the work the writer discusses various 

 phenomena occurring at Vesuvius in relation to those at Monte 

 Pelee. He describes the avalanches of dry volcanic dust and 

 ashes caused by the accumulations on the steep sides of the cone. 

 These leave ravines behind them which become accentuated by 

 rain wash and this produces the curious umbrella-like relief of 

 the mountain. 



In conclusion a study of the facts obtainable of the eruption of 

 '79, which destroyed Pompeii, leads the author to the view that 

 this phenomenon was of the regular Yesuvian type, and that the 

 destruction, occurring through a period of several days, was 

 caused by the excessive fall of cold, or at least only warm, ashes 



