BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 23, pp. 493-516 October 22, 1912 



GEOLOGICAL RECONNAISSANCE IN NORTHEASTERN 



NICARAGUA ^ 



BY OSCAR H. HERSHEY 



{Presented before the Society December 27, 1911) 



CONTENTS 



Page 



Introduction 493 



Quaternary deposits 497 



Detailed descriptions 497 



Modern alluvium 507 



Soulala formation 507 



Saclin formation 507 



Tertiary rocks 508 



In general 508 



Andesite 508 



Rhyolite 512 



Diorite (?) 514 



Miscellaneous 514 



Pre-volcanic sedimentaries 515 



Age of the igneous rocks 510 



Introduction 



In the spring of 1910 the writer accompanied a party of mining engi- 

 neers to the Pis-Pis mining district of Nicaragua. Landing at Cape 

 Gracias a Dios, we ascended the Wanks, Waspuc, and Pis-Pis rivers, an 

 estimated distance of 225 miles to the mines. Fifteen days were spent 

 in the district, and then two of us descended the Tunkey, Banbana, and 

 Prinzapulca rivers an estimated distance of 195 miles, to tlie mouth of 

 the latter. Several days were also spent at Bluefields. Although the 

 trip was too rapid to permit of detailed geological work except in the 

 vicinity of a few mines, a series of observations were made that seem 

 worthy of record. 



Thomas Belt, who went to Nicaragua in 1868 to superintend the min- 

 ing operations of the Chontales Gold Mining Company, describes^ the 



1 Manuscript received by the Secretarj' of the Society December 0. 1011. 



2 The Naturalist in Nicaragua. Tublished in London in 1874. (493) 



