METAMORPHIC AND IGNEOUS ROCKS. 



Specimens of lavas. 



87 



TUFFACEOUS ROCKS. 



The collection contains specimens of typical unsorted tuffs, of water-laid 

 sandstone consisting largely of volcanic material, and of metamorphic 

 rocks that may be altered tuffs. The last named are described under 

 "Metamorphic sedimentary rocks," page 83. 



Unsorted tuffs were found in the provinces of Puerto Plata, Azua, Bara- 

 hona, Santo Domingo, and La Vega. In composition they are andesitic 

 and basaltic. They vary widely in degree of alteration and range in color 

 from whitish to dark green or red. 



Tuff sandstones in which feldspar crystals are somewhat concentrated 

 by current action were collected in the provinces of Santiago, Pacificador, 

 and Puerto Plata. These are olive-green. 



