T. A. Jag gar — Initial Stages of the Spine on Pelee. 39 



theory of Lacroix supposes a "lava" to have risen from the 

 deep regions to furnish material for the spine. This "lava," 

 nearly congealed, "seems to have been pushed up bodily into 

 its present position, and to be maintained there, somewhat like 

 the stopper in a bottle, by friction against the sides of the neck 

 and by the expansive forces underneath."* There can be no 

 question of the evidence that shows the spine to have been 

 pushed up in a semi-solid condition through fissures in the cone 

 of debris. We may ask, however, this question, — may not the 

 half-molten substances be a superficial product, resulting from 

 the mechanical and thermal conditions that governed the build- 

 ing of the cone ? 



The writer's reasons for opposing the "lava" hypotheses are 

 twofold : (1) None of the ejecta of Pleistocene times in the 

 Caribbees are true lavas ; (2) Even the more ancient geologic 

 sections show few flows. If lavas are to flow from Pelee at 

 this time, then these eruptions inaugurate a new era. This 

 is improbable, for there have been eruptions in these islands 

 averaging once in twenty-three years for over 300 years of 

 human record, and the eruptions of the unrecorded previous 

 centuries left no lava flows on the present or recent topography. 

 The ejecta collected from the present and past historic eruptions 

 are fragments of ancient andesites and basalts. 



Theory of Origin of Spine. 



The following is a suggested explanation of the origin of the 

 spines, which does not require a flowing lava to rise into the 

 throat of the volcano from deep-seated sources: — 



The spines are small compared to the volume of material 

 which has fallen back into the crater from many successive 

 eruptions. This material Alls not only the crater-gorge of the 

 Piviere Blanche, but deep fissures of unknown size beneath the 

 present cone. Such fissures have been enlarged below with 

 every eruption, while at the same time bombs have been 

 heaped upon the cone above. 



The rocks ejected were observed to become more incandescent 

 with successive eruptions and much of that which fell back on 

 the cone consisted of large fragments half molten on the surface ; 

 there was much finer material mixed with these. 



Accumulation of this pasty incandescent material with each 

 new eruption produces increased pressure from above, and by 

 conduction and radiation the heat is probably concentrated. 

 The outer portions of the cone become crusted, a blast of hot 

 gases and the steam traverses the open passages, and both 



*Hovey, loc. cit., p. 278. 



