462 «Hague and Iddings—Rocks of the Great Basin. 
same ingredients. 
partite, —This rock in distinction from nevadite 1s char- 
acterized by a small number of porphyritic crystals imbedded 
basalt and hypersthene-andesite, between hornblende- and 
-pyroxene-andesite, or any two closely allied species. Indeed, 
where the conditions for the developement of sanidin seem 
favorable it usually comes in strong force; the change from 
plagioclase to orthoclase being in many cases quite marked. — 
* Microscopical Petrography, p. 8. + Ibid, p. 8. 
{ H. Rosenbusch, Neues Jahrbuch fiir Mineralogie, 1882, vol. ii. f 
§ It seemed necessary to enter somewhat fully into an explanation as to the 
position of nevadite, partly because its exact relations to other volcanic lavas has, 
in our opinion, been misunderstood, and partly because in the paper on the “ Vol- 
’ to bé classed wi 
reat Basin which form such characteristic extrusions in the state of Nevada, 
