84 



PROCEEDINGS OF THE WASHINGTON MEETING 



Approximately 10,000 fossil specimens were obtained from the "older" and 

 "younger" series of formations. In certain localities algae, foraminifera, and 

 corals were collected from the limestone members in the "older" series. They 

 suggest Cretaceous age. The larger portion of the collection, however, was 



STAGE 



ELEVATION 



EROSION 



SUBSIDENCE 



DEPOSIT/ON 



COMMENTS 



xrv 





Delta and Coastal 

 Terraces 





Coastal Barriers, Dune 



Sand, San Juan Formation 



River Flood Plains 



Present 



xm 



Slight Uplift 



Rejuvenescence of 

 Rivers 







Partial Withdrawal of 

 Sea from Platform 



xu 









Alluvial and Coastal 



Conglomerates, 



Sands and Shales 





XT 







Marginal Transgression 

 of the Sea 





5? 'Cycle of Erosion 

 incomplete 



X 





Inauguration of present 

 Upland Dissection & Incept- 

 ion of present River Valleys 







IX 



Uplift 









Tilting Sedimentary 

 Series, Po/ding&fau/fing 



WL 





Development of 

 Peneplain 







2 1 Cycle of Erosion 

 incomplete 



w 



Uplift 









Tilting Sedimentarv 

 Ser/es.roldingS faulting 



w 









Local Deposition of 



green Shales and 



Limestones 



Long Duration 



V 







Subsidence affecting 

 greater Portion of Island 





Unconformity between 

 'o/der'S 'younger Series 



I st Cycle of Erosion 



w 





Development of 

 Peneplain 





Deposition beyond 

 Edge of present P/at- 

 9 'form 



m 



Uplift 









Injected Porphyries, etc 



affecting both Igneous & 



Sedimentarv Series 



R 









Local Deposition of Conglomer- 

 ates, black Shales, interbedded 

 Tuffs and Breccias. and Lime- 

 stones on submeroed P/altorm 



Long Duration 



i 



Initial Volcanic Cones 











Figure 1. 



Chester A Reeds. December 1915 



-Stages in the geologic History of Porto Rico 



gathered from the lignitic shales and white limestone of the "younger" series. 

 The sea-urchins collected from these beds indicate late Eocene or early Oligo- 

 cene age. It would be premature to assign ages to the various formations and 

 stages in the geologic history of Porto Rico before this large collection of 

 fossils has been worked up. 



Presented in abstract extemporaneously. 



Discussion 



Mr. Edwin T. Hodge : The "older series" in Porto Rico has long been looked 

 on as non-fossiliferous, and therefore of undeterminate age. East summer, 

 during my investigation in the south central portion of the island, I was fortu- 

 nate enough to find some fragmentary fossils, which, it is true, do not consti- 

 tute a whole flora or fauna, yet are sufficient to establish with certainty the 

 following statements : 



At the crest of the Sierra Oayey, the rocks of which lie near the base of the 

 series, I found the calises of two OladopJiyllia furcifcra characteristic of the 



