VOLCANIC EKUPTIONS ON MAKTINIQUE AND ST. VINCENT. 333 



surface water to hiohly Jieated rocks, so that an a])i)arently coniplete 

 sequence may V)e observed V)etiWeen the escape of steam from hot 

 del)ris and the dischar<«(>s from true volcanic conduits. It is thus seen 

 that the discovery of th(^ crucial test asked for is ditticult, and the final 

 decision, if one is reached, nuist rest on a judicial ])alancino- of all the 

 evidence and the weij^ht to l)e given to the judgment of individual 

 observers. An insti'uctive fact furnished l)y the pseudocraters (even 

 when the larger and, as some persons may think, questionable exam- 

 ples are not considered) which has a bearing on the theories of the 

 ultimate causes of volcanic eruptions is the close similarity and, in 

 fact, identity that exists between the explosions due to surface water 

 gaining access to beds of hot debris and the explosions during primary 

 eruptions in the sunuuit portions of true volcanic conduits. In the 

 former instances surface water descends into hot-rock debris; and, 

 from the fact that water is present in the superficial portion of the 

 earth's crust, it seems equally manifest in the latter instance that 

 highly heated rock rises fi'om deep within the earth and meets the 

 surface waters. In each instance steam explosions result. 



The conditions favoring the ociairrence of pseudo-eruptions and the 

 character of the topographic changes produced by them are clearly 

 shown in the sketch and section forming fig. 2, PI. II, which accompa- 

 nies an instructive article on the "Secondary Phenomena of the West 

 Indian Volcanic Eruptions,'"' by G. C. Curtis," pul)lished since the 

 pi'esent essay appeared. Some of the secondary craters, or "ash- 

 geyser cones," on Martinique and St. Vincent are stated l)y Curtis 

 to ])e 4U feet high and IHO feet in diameter, with slopes averaging- 

 's^ to 3(»-. 



Y((r!<it!<m t n iJic ci-KptloHs of the prima rij crater^. — The variations 

 presented by the steam colunms that ascend from acti\e volcanoes — 

 of which the so-called pine tree of Vesuvius is a well-known exam- 

 ple — and which in many instances afford the most spectacular of the 

 awe-inspiring phenomena associated with them, have been described 

 by several observers who have recently visited Martinique and St. 

 Vincent, but most graphically l)y Georg'e Kennan. The variations 

 referred to are indicative of what takes place in an active crater and 

 in the upper part of the conduit leading to it, and furnish evidence in 

 reference to the changes there in progress. A classification of the 

 various phases presented 1)}^ the steam colunm rising from Mont Pelee 

 lias been presented b}^ the gifted traveler just referred to, which is 

 instructive: 



" The vapor column ascending from Mont Pelee," writes Kennan, 

 "varies greatly from day to day and sometimes from hour to hour, 

 not only in density, 1)ut in color, form, and general ai)i)earance. In 

 its varying aspects it may be desci'ibcd as follows: 



" I. The \a})or of (|uiescence: A slowly ascemling colunm of })ure 



«The Journal of Geology, Vol. XI, February-March, 190;}, pp. 199-215. 



