434 AXXALS XEW YORK ACADEMY OF SCIEXCES 



The areal geology of the district was next studied. The formati- ins 

 were generally subdivided as follows : 



Yotmger series : 



E^cent deposits — alluvium — San Juan lime sand. 

 Tertiaiy deposits — limestones and shales. 



Older series : 



A complex of pyrocla^stic tuffs, ashes and breccias grading into essen- 

 tially hydroclastic sandstones, shales, conglomerates and lime- 

 stones, intiTided by numerous igneous masses of great variety, all 

 of which are probably pre-Tertiary. 



The areas of economic import-anee are : 



The gold mines south of Corozal. 



Auriferous quartz stringers in the older series, usually occurring in 

 fractured tuffs. 



The gold placers near Corozal. 



The streams in this vicinity afford some gold and occasional particles 

 of platinum. 



The copper prospects in the barrio of Pasto. 



Impregnations along crushed zones in a porphyritic intrusion. 



Since rerurning from the field the writer has been engaged in a micro- 

 scopic study of the petrogenetic relations of the various formational units 

 and in the determination of the more important fossils collected in the 

 Tertiary formations. 



Mr. Hodge discussed the physiographic history of the Coamo-Guayama 

 district located on the south central portion of Porto Eico and which 

 recorded the following events : (1) peneplanation, (2) burial, (3) uplift 

 and development of a consequent drainage on the limestone coastal plain 

 which covered part of the island, (4 ) attempt on the part of streams to 

 attain sti'uctural adjustment, and finally, (5) recent uplift. Because of 

 deep residual soil, few outcrops and absence of fossils, accurate detailed 

 stratigraphic correlation proved impossible, but in a large way the rocks 

 have been grouped and their succession worked out. The bedded forma- 

 tions, a^ide from minor irregtdarities. dip 60° -70° south and strike north 

 40° west throughout most of the area, excepting the southeast portion 

 where they assume a synclinal structure. The most characteristic feature 

 of the area consists of the hundreds of separate and distinct intrusions 

 and extrusive rocks with their associated tuffs and breccias. These pyro- 

 genic rocks are mostly of an andesite composition and all highly altered 

 to carbonates, so much so that previous workers have considered many of 



