516 O. H. HERSHEY GEOLOGICAL RECONNAISSAKCE IK NICARAGUA 



stones^' in the Santo Domingo district doubtlessly correspond to the 

 extrusive andesite and hard ribs of augite andesite in the Pis-Pis district. 



Age of the igneous Rocks 



In age the rocks of the Pis-Pis district are probably mid-Tertiary. 

 This statement is based on the fact that similar rocks elsewhere in Cen- 

 tral America are known to be of that age, and on the fact that the erosion 

 of the country shows that volcanic activity ceased earlier than the 

 Quaternary era or even the latter portion of the Pliocene period. 



