WES T INDIA N VOL CA NIC ER UP TIONS 



213 



in topographic form and phenomena of eruption. Professor 

 Russell asks:' "What is the crucial test by which a true crater 

 may be distinguished from a pseudo-crater?" as he terms these 

 secondary craters. Five characteristics were noted : first, loca- 

 tion — the ash-geyser crater occurs persistently within the 

 streams or the deltas; second, composition — the walls are con- 



Fig. II. — Ash cone topography and dissected ash cone lying in the present 

 stream channel — Wallibou river. (Arrows point to cone). 



structed entirely of fragmental material and not of old bedrock 

 (the structural layers of the volcanic cone as observed on the 

 rims of the primary craters); third, method of eruption — erup- 

 tion occurs only in time of water accumulation ; fourth, tempera- 

 ture — a relatively low temperature of ejecta ; fifth, size — the ash- 

 geyser cone is a small fraction of any true lateral crater observed. 

 I am inclined to account for both the island discovered off the 

 river Blanche on May 23,^ and which had disappeared on return 



^National Geographical Magazine, Vol XIII, No. 12, p. 416. 

 * R. T. Hill, Century Magazine, September, 1902. 



