54 



CONVEXITY OP THE PLAIN OE MALPAIS. [Cii. XXVII 



'0111 them 



plain. This mass was still in a heated state^ the tempe- 

 ratnre in the fissures being on the decrease from year to year 

 bnt in 1780 it was still sufficient to light a cigar at the depth 

 of a few inches. On this slightly convex protuberance the 



slope 



must form an angle of about Q"" with the 



mounds 



to 9 feet high, which, as well as large fissures traversino* 

 the plain, acted as fumeroles, giving out clouds of sulphurouo 

 acid and hot aqueous vapour. The two small rivers before 

 mentioned disappeared during the eruption, losing themselves 



Fig. 89. 



a. Summit of JoruUo. b, c. Inclined plane sloping at an angle of G° from the base of the cones. 



3 eastern extremity of the plain, and 



gs at its western limit. 



)/ the convexity of the plain of Malp 



•Hnmboldt 



attributed the convexity of the plain to inflation from below ; 

 supposing the ground, for four square miles in extent, to 

 have risen up in the shape of a bladder to the elevation of 

 650 feet above the plain in the highest part. But 



Mr 



may 



more 

 from 



the different orifices, and principally from JoruUo, 

 ■united into a sort of pool or lake. As tliey were poured fortli 

 on a surface previously flat, tli e j would, if tlieir liquidity was 

 not very great, remain thickest and deepest near their source, 



diminish 



fc 



from 



space which they covered. Fresh supplies were prohably 

 emitted successively during the course of an eruption which 

 lasted more than half a year ; and some of these, resting on 

 those first emitted, might only spread to a small distance 

 from the foot of the cone, where they would necessarily 



The average slope of the 



accumulate to a great heio-ht. 



ome-shancd vol^nnns r>f -i 



almost exclusively of lava, with scarce any scorite, is between 

 6° 30' and 7° 46', so that the inclination of the convex mass 



Scrope's explanation (see 



around Jorullo, 



Mr 



\ 



CS' 



S- 





g 



Tb 



six 



ci 



ofte 



ram 



) 



hicl 



w 



fire ' 



prodi 

 small 

 byH 



uatu] 



COllt] 



istl] 



valli 



exa: 



the 

 and 



■a: 

 latioi 



tliict 



r 



aceni 

 with 



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ai 



