PRODUCTS OF THE ERUPTIONS . 251 



features. These water products of Pele were manifest in several ways 

 during the various stages of eruption. During the preparatory stage 

 for several days before the fatal catastrophe the streams descending 

 from Pele toward Saint Pierre were swollen to thirty times the volume 

 ever known from freshets, and, for a time after the catastrophe, flowed 

 volumes of hot mud. Later, in the free working stage of the volcano, 

 tremendous clouds of steam discharged from the summit and dissipated 

 into the atmosphere. Messrs Flett and Anderson, of the British Com- 

 mission, have clearly shown that the steam or water was largely con- 

 tained within particles of lapilli themselves, which emitted vapors on 

 rolling down the crater slopes. 



Gas products. — From the first the writer maintained that one of the 

 most essential scientific questions presented by the West Indian erup- 

 tion was the quantity and character of the gases which accompanied 

 them and the light they threw on the nature and history of vulcanism 

 in general. As will be seen in the last chapter of this paper, the question 

 of gases is still the most important one in the whole subject of vulcanism.* 



Most of the gases of vulcanism are combined into solid material before 

 reaching the exit. The remainder are difficult to study, as they escape 

 from an active and dangerous volcano. Those gases which remain free 

 sufficiently long to be determined, uncombined with other substances, 

 are merely the expiring after products. Some of these may be readily 

 detected by the senses, others by collecting them from fumaroles; still 

 others are detected only by the products of sublimation ultimately found 

 in the rocks and crevices of the volcano after it has become sufficiently 

 cool for study. It is also probable that many other gases escape which 

 are not discernible by any known method. 



Only the evidence concerning these expiring gases in the surface erup- 

 tions can now be presented, reserving the discussion of their larger occur- 

 rence within for the final chapter. Dana has said that " the chief vapor 

 or gas coming from volcanic lavas is sulphurous acid (S0 2 ), and with it 

 may be hydrogen and nitrogen." This statement may not be literally 

 accurate, for it is probable that hydrogen and oxygen far excel all other 

 gases in quantity, but sulphurous acid (S0 2 ), having the smell of sulphur, 

 is among the most apparent and detectable of the vapors. It is always 

 present. The volcanic vents of the Caribbee islands all yield sulphurous 

 vapors. Some of them, as in Dominica and Saint Lucia, deposit the 

 sulphur in considerable quantities. The very name of these quiescent 

 craters, which are called " soufrieres," attests the sulphurous nature of 



*According to Geikie the pases of the following elements have been found in volcanic emana- 

 tions : oxygen, hydrogen, sulphur, chlorine, nitrogen, carbon, fluorine, and iodine. From the sub- 

 imates and combinations of gases, potassium, iron, copper, lead, borax, and sodium have alio 

 been found. 



XXXIV— Bull. Geol. Soc. Am., Vol. 16, 1904 



