VOLCANIC PRODUCTS. 



353 



Bourbon, where the stream, flowing over a precipice, has let t heavy pen- 

 dent masses resembling the drippings of a guttering candle. Another 

 illustration of the forms produced by very viscid lavas is afforded by 

 the so-called " mamelons" of the island of Bourbon. The flow of rapid 



Fig. 4,-Vesuvian Lava-Stream of 1858, exhibiting the Peculiar "Ropy" Surfaces of 

 Slowlt-moving Currents. (From a Photograph.) 



currents is generallv accompanied with the disengagement of vast quan- 

 tities of steam, and" this, doubtless, has much to do with the formation 

 of the cindery projections which characterize the cooled surfaces of such 

 streams. Little parasitic volcanoes are often formed on the top of the 



VOL. XX.T-l 



