442 REACTION OF THE INTERIOR OF THE EARTH 



like trachytes of Yana-Urcu, near Calpi, at the foot of 

 Chimborazo ( 625 ), as well as those belonging to what is 

 called " la reventazon del volcan de Ansango," ( 626 ) con- 

 tain no olivine. It was only in the great brownish-black 

 lava-stream, with a curled scoriaceous surface and cauli- 

 flower-like intumescence,, up which we made our way to 

 the crater of the volcano of Jorullo, that we found 

 small grains of olivine. ( 627 ) The very general scarcity 

 of this mineral in the more recent lavas and in the 

 greater part of the trachytes, becomes less surprising 

 when we remember that, however essential olivine may 

 appear to be, yet (according to Krug von Nidda and Sar- 

 torius von Waltershausen) there are in Iceland and in 

 the German Ehongebirge basalts without olivine, which 

 can scarcely be distinguished from the basalts having 

 olivine. In earlier times it was usual to call the former 

 "trap" and " wacke," and in more recent times, "ane- 

 masite." ( 628 ) Olivines, which are sometimes found as 

 large as a man's head in the basalts of Kentieres in 

 Auvergne, also attain, in the Unkel quarries, which 

 were the subject of my first youthful studies, a diameter 

 of more than 6 inches. The fine often-polished hyper- 

 sthene of Elfdal in Sweden, a granular mixture of 

 hypersthene and labradorite, which Berzelius has de- 

 scribed as syenite, also contains olivine ( 6 - 9 ), as does (a 

 still more rare case) the phono] ite of the Pic de 

 (jrriou ( 63 ) in the Cantal. According to Strom eyer, 

 olivine is very constantly accompanied by nickel ; and 

 Kumler has discovered in it arsenic ( 631 ), a metal which 

 has very recently been found to be widely distributed 

 in mineral springs and even in sea-water. I have 

 spoken earlier of the occurrence of olivine in meteoric 



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