Volcanic Disturbances in West Indies 



295 



desite. Later came basalts from craters 

 about the base of the cone marking the 

 site of the principal vent, and these were 

 often succeeded in the principal vent by 

 dacites or rhyolites. The series is well 

 illustrated at Lassen Peak, less com- 

 pletely at Mt Shasta, but especially well 

 in Mt Mazama, about Crater Lake. 

 With this succession in mind we ma3 r 

 surmise the order in the volcanoes of 

 Martinique and St Vincent. 



LAVAS OF CARBET PEAK 



Upon the northern end of Martinique 

 are two peaks which have been vol- 

 canoes, and each has its succession of 

 lavas. Mont Pelee is still active, but 

 Carbet, according to Mr Hill, has long 

 since ceased erupting and is now deeply 

 eroded. 



From Mount Carbet seven specimens 

 were obtained. Three (Nos. 9, 12, and 

 15) from the base are hypersthene an- 

 desite, but one of them (15) contains 

 some prominent crystals of hornblende. 

 From a ravine in the upper slope of the 

 plateau comes a well-marked hornblende 

 andesite (No. 3^) and a hypersthene 

 andesite (3a), with a trace of augite, 

 while the ' ' material of the peaks ' ' is 

 (4) dacite ; but, judging from the order 

 among the volcanoes of the Cascade 

 Range, the dacite is possibly youngest. 

 Against this view, however, is the very 

 altered condition of one specimen (20) 

 of dacite. Considering that the volcanic 

 vent of Carbet has furnished not only 

 andesites with hornblende and hyper- 

 sthene, but also dacite, basalts might 

 well be expected to occur on the periph- 

 ery of the same vent. 



LAVAS OF MONT PELEE 



The series of lavas of Mont Pelee is 

 less complete, but how much is due to 

 lack of complete collection is not known. 

 Nine specimens were obtained, among 

 which three (2, 5, 13) are hornblende- 



bearing hypersthene andesites, one 

 augite hypersthene andesite, and four 

 hypersthene andesites, one of which 

 belongs to the fresh eruption. The dif- 

 ferentiation of the magma has not yet 

 completed its cycle and there is no defi- 

 nite evidence that it ever will. 



LAVAS OF LA SOUFRIERE, ST VINCENT 



The number of specimens from St 

 Vincent is small. They all belong to 

 hypersthene andesites, but are remark- 

 ably abnormal in containing olivine. 

 How general this feature may be can 

 only be surmised from the number of 

 olivine-bearing specimens. Three of 

 the four specimens contain olivine, and 

 the fourth ma}' contain it also, although 

 not shown in the thin section. The 

 olivine was one of the early minerals to 

 cr3'stallize in the magma, and its occur- 

 rence here may be attributed to some 

 peculiar condition. It recalls the more 

 or less sporadic occurrence of quartz in 

 basalt, which in some cases,* for exam- 

 ple the Cinder Cone, 10 miles northeast 

 of Lassen Peak, California, becomes a 

 general feature of the erupted mass. 



For more thorough study of the petro- 

 graphy of the recent eruptions of Mar- 

 tinique and St Vincent we must look to 

 Prof. T. A. Jaggar, who is spending 

 sufficient time upon the ground to make 

 extensive and complete collections. 



VOLCANIC SMOKE AND ASHES 



Volcanoes are popularly referred to, 

 even in scientific circles, as " smoking " 

 and ejecting " ashes," but it should be 

 understood that the terms do not express 

 the same process or product ordinarily 

 associated with chimneys. 



Some form of organic carbon com- 

 pound, as wood, coal, oil, or gas, is the 

 common source of light and heat, and 

 the smoke results in large part at least 



*U. S. Geological Survey, Folio 13 and Bul- 

 letin 79. 



