428 REACTION OF THE INTERIOR OF THE EARTH 



If, as has often been done, it is desired to restrict the 

 name of trachyte (for the sake of conformity with its 

 earliest application to the rocks of Auvergne and of the 

 Siebengebirge near Bonn,) by applying it exclusively to 

 a volcanic rock containing felspar (particularly Werner's 

 glassy felspar and Kose's and Abich's sanidine), the 

 result is unfruitfully to rend asunder those intimate 

 links between different volcanic rocks which conduct 

 to higher geological views. Such a restriction might 

 justify the expression, " that Etna, rich in labradorite, 

 has no trachyte ; and, according to it, my own collec- 

 tions would be held to prove that " none of the almost 

 countless volcanoes of the Andes consist of trachyte, 

 and even that the mass of which they are composed 

 should 4 be called Albite, and, therefore, inasmuch as at 

 that time (1835) all oligoclase was erroneously supposed 

 to be albite, that all volcanic rocks would have to be 

 designated by the general name of Andesite (consisting 

 of albite with little hornblende). "( 592 ) The impressions 

 which I brought back from my travels of that which, 

 notwithstanding diversity of mineralogical composition, 

 all volcanoes possess in common, have been confirmed 

 by Grustav Rose, who, in accordance with the views and 

 evidence unfolded in his fine memoir on the felspathic 

 group ( 593 ), has, in his classification of trachytes, regarded 

 orthoclase, sanidine, the anorthite of the Somma, albite, 

 labradorite, and oligoclase, in a general point of view, 

 as the felspathic portion of volcanic rocks. 



Short denominations, purporting to contain defini- 

 tions, often tend in various ways, in the study of rocks 

 as well as in chemistry, to produce obscurity and not 

 unfrequently confusion. I was myself for some time 



