May 6, 1898.] 



SCIENCE. 



623 



does not consider it advisable to apply the 

 same names to the rocks of the two local- 

 ities on account of minute differences and 

 overlaps in chemical and mineral composi- 

 tion. 



as no doubt this hypothetical third set of 

 lavas v?ould likewise overlap the flows in 

 Yellowstone Park and in Italy. 



Two of the names used in the above table, 

 namely, trachydolerite and labradorite- 



It is safe to assert that if a petrographer 

 •were given some specimens of similar in- 

 termediate lavas from an entirely new field 

 .to name he would find dilficulty in choos- 

 ing between the names adopted for the Yel- 

 lowstone Park lavas and the names adopted 

 for the Italian lavas, and the tendency 

 ■would be to adopt still a third set of names, 



trachyte, give at once to the reader a defi- 

 nite idea of the composition of the rocks. 

 The term trachandesite* used by Dr. Ran- 



* Since writing this Dr. Eansome has changed his 

 name to a more specific name, kiiiie. But as he re- 

 gards bis rocks as intermediate between trachyte and 

 andesite the statements here made regarding them 

 still apply. 



