296 The National Geographic Magazine 



from the imperfect contribution of the 

 carbon, which is black. The heat 

 evolved is of combustion in the oxygen 

 of the air, and the ashes are the residue 

 left after the separation of the carbon 

 compounds. 



In the volcanic process, however, 



there is no combustion of carbon, nor 

 black smoke due to unconsumed carbon. 

 The so-called smoke is chiefly steam 

 clouds rendered dark or black by lapilli, 

 sand, and dust, particles of solid rock 

 matter such as those that fell at Barba- 

 dos from St Vincent. 



CHEMICAL DISCUSSION OF ANALYSES OF 

 VOLCANIC EJECTA FROM MARTI- 

 NIQUE AND ST VINCENT 



By W. F. Hillebrand 



SEVERAL, of the chemical anal3'ses 

 of the foregoing paper by Dr 

 Diller were only completed after 

 his report had gone to the printer, and 

 are hence not utilized in his discussion. 

 There are several features connected 

 with these and other analyses that have 

 appeared in print which are suggestive, 

 and it may be worth while to call atten- 

 tion to them at this time. The data 

 at hand are not sufficient to warrant 

 positive conclusions, but on their face 

 certain probabilities appear to be indi- 

 cated. 



Aside from the five analyses made by 

 chemists of the Geological Survey, the 

 only one of much value that has come 

 under my observation is that by Dr Pol- 

 lard in Nature, page 130 (No. 5 of Dr 

 Diller' s table). This, while less sili- 

 ceous than any of the others, and high 

 in lime and magnesia, is in nearly every 

 respect confirmatory of the others of 

 like type. The exception will be re- 

 ferred to later (page 299). The three 

 following analyses are incomplete and 

 unsatisfactory, and only of service in a 

 general way. For convenient reference 

 they are reproduced here : 





(a) 



(*) 



(0 



SiO, 2 



53-34 

 30.68 



10.47 



4.12 



51.60 

 / 21.12 

 \ 9-28 

 9.07 

 396 

 o.59 

 o.8t 

 089 



•19 

 1.20 

 1.29 



53 4° 



A1. 2 3 \ 



Fe 2 0, ( 



CaO 



21.00 

 9 5o 

 9.70 



MgO 



2. CO 



Na„0 



2 33 



K.,6 





0.85 



so 3 . 





0.90 



s 



•17 

 Trace. 



0.90 



P,0 5 



25 



Undet 







98. 7 s 



100.00 



99-93 



a. " Mineral dust from the Martinique erup- 

 tion," which fell on board the Alesandro del 

 Bueno, about 100 miles from St Pierre (date 

 and location not given). Science, June 6. 



b. Volcanic dust which fell over the Barba- 

 dos on May 8. Chemical News, June 13. 



c Volcanic dust collected from deck of 

 steamship Roddam on her arrival at St Lucia. 

 Chemical News, June 13. 



If we consider now the six most com- 

 plete analyses, those of Diller' s table, 

 they appear chemically to fall into two 

 groups, one from Pelee, on Martinique, 



