38 T. A. Jaggar — Initial Stages of the Spine on Pelee. 



The Spine of 1903. 



Comparing this spine with the greater one figured by Hovey* 

 from photographs taken in March, 1903, it will be seen that it 

 faces in the opposite direction, i. e. the steep scarp in Hovey's 

 pictures faces west, in our photograph it faces east. In both 

 cases there is a long curved constructional slope on one side and 

 a broken cliff of destruction the other. Hovey has pointed 

 out that the later spine was probably the product of conditions 

 developed after August 30th, 1902. The two eruptions of 

 July 9th and August 30th, 1902, were sufficiently violent to 

 destroy the spine observed July 6th, by the present writer. 



The steep cliff is clearly in both cases a destructional surface 

 from which material has fallen away. The evolution of the 

 later spine as observed by Major Hodderf , changing from the 

 "lighthouse" shape to the "church steeple" (shark's tin) shape, 

 seems to the writer to imply the blowing off or caving in of 

 one side of a conical mass at first symmetrical about a central 

 vent. This would account for the absence, noted by Hovey;}:, 

 of any "definite conduit through the spine itself," and the 

 occurrence of heavy outbursts "from the southwest side of the 

 cone near, the base of the spine". The channel for such out- 

 bursts, at the base of the steep side of the spine, is the original 

 central conduit of a domical mass which has completely caved 

 in on one side, leaving the infacing spine as a half broken- 

 down remnant. The process of breaking down may be grad- 

 ual, and the upthrust from below may continue to act on the 

 half destroyed residual spine. This will account for gradual 

 changes of shape and fluctuations in elevation of the spine. The 

 striated surface, if this explanation be correct, should be found 

 on all sides of the monolith during the continuance of the 

 "lighthouse" stage. This stage may be restored to the profile 

 shown in the photographs by imagining the smooth curve 

 repeated on the steep side of the spine so as to give it a sugar-loaf 

 shape. Thus in July, 1902 (figs. 2 and 3), the east side of the 

 sugar-loaf had been blown away or had flaked off ; in March, 

 1903, the west side had been removed as shown in Hodder's 

 diagrams. § 



Granting that these horns are broken remnants of hard cone- 

 shaped protuberances from the new pile of debris in the crater- 

 gorge, there remains the question of- the origin of these protu- 

 berances. They have dike ribs extending from them, and are 

 composed of hard rock,, fissured and glowing at times, but with- 

 out associated lava streams of any sort. The cumulo-volcano 



* This Journal, figs. 1 to 7, October, 1903. 



f Hovey, loc. cit. pp. 273-275, and tigs. 2 and 3. 



\ Loc. cit. p. 279. $ Loc. cit. 



