RECENT WORK ON VOLCANOES 91 



The combined nitrogen appears to be the result of the action 

 of hydrogen on metallic nitrides. Silvestri (10) actually found 

 nitride of iron on the surface of lava from Etna. Metallic 

 nitrides, when heated with hydrogen or water-vapour, yield 

 ammonia, and this would readily form sal-ammoniac with the 

 hydrogen chloride of the exhalations. 



So far for the gases given off from volcanoes ; the types of 

 volcanoes that yield them are those that have been known since 

 the earliest times. In Iceland and in the Snake River Plains of 

 Idaho, there are types that are entirely new to scientific 

 literature. The commonly known types are mostly those 

 connected with the folding in the earth's crust. In the 

 Mediterranean and West Indies the volcanoes lie uniformly 

 at the back of the great folds ; in the JEgean and in Mount 

 Ararat, the volcanoes lie in a "Schaarung" or knot where two 

 systems of folds meet. In Kasbek and Elbruz the cones lie in 

 the centre axis of the folds, while in the Andes they are related 

 at any rate to the folds in that they follow lines of weakness 

 determined for them by the curvature of the strata. In Iceland 

 and in Idaho, the whole country for thousands of square miles 

 has been a seething mass of lava and the vents rise through it 

 as if drilled by gases that have come through a semi-viscid 

 magma without any sort of order. The special types repre- 

 sented here are the explosion rings, the slag craters, and the 

 buckler cones; then there are the fissure eruptions which are 

 well known and the volcanoes of block-uplift which are new to 

 science. Although the description of these is due principally 

 to Dr. Hans Reck from examples in Iceland, they were being 

 investigated by Walther von Knebel at the time of his death. 

 The latter with two companions had ascended the most 

 wonderful of all volcanoes, the Askja, camping on the shores of 

 the lake that lies in the south-eastern corner of the caldera on 

 top. On the fatal day, July 10, 1907, he and his artist friend 

 Rudloff had taken a collapsible boat and had gone for a row ; 

 when the third member of the party returned to camp there 

 was no sign of the others. A relief party was immediately sent 

 out, but nothing could be found of the missing ones. Dr. Reck 

 the following year visited the place and spent eleven days 

 searching for a clue to the mystery; the only result was the 

 surmise that an avalanche of rocks had overwhelmed the frail 

 boat and its freight. 



