90 PROCEEDINGS OF THE AMHERST MEETING 



GEOLOGY OF COSTA RICA 

 BY E. B. BRANSON 



(Abstract) 



The dominant topographic feature of eastern Costa Rica is a high mountain 

 range that trends northwest-southeast. The country east of this range is 

 made up of piedmont alluvial fans. In a few places remnants of Cenozoic 

 sedimentaries are preserved. In the valley of the Reventazon River the Ce- 

 nozoic sediments are more than 10,000 feet thick and range from Eocene up 

 in age. The dominant activity of recent times has been vulcanism, and nearly 

 all of the sedimentaries are extensively intruded by recent lavas. Volcanic 

 ash deposits of Fliocene or Pleistocene times are widespread. The seas seem 

 to have extended across this region during most of the Cenozoic. Some of 

 the formations are highly fossiliferous. 



Presented extemporaneously, with lantern-slide illustration. 

 Adjournment was taken about 12.30 o'clock p. m. 



TITLES AND ABSTRACTS OF PAPERS PRESENTED BEFORE THE AFTERNOON 

 SESSION AND DISCUSSIONS THEREON 



The Society divided into two sections Wednesday afternoon. The first 

 was presided over by Vice-President Woodworth, and Edmund Otis 

 Hovey acted as its Secretary. The following program was offered: 



THE ANDEAN GEOSYNCLINE 

 BY CHARLES SCHUCHERT 



(Abstract) 



The nature of the Andean geosyncline and of the old land that lay to the 

 west and is now sunken into the abyss of the Pacific was briefly described 

 and contrasted with that of the Appalachian geosyncline. These two geo- 

 synclines, with their periodically rising bordering lands, are markedly differ- 

 ent in their quantitative movements. 



Presented extemporaneously. 



Discussed by F. P. Shepard, W. M. Davis, K. F. Mather, T. Wayland 

 Vaughan, and W. H. Bucher. 



Discussion 



Dr. Shepard: Might I ask Professor Schuchert whether it would not be 

 possible for the forelands to be much narrower than 250 miles and still pro- 

 duce the required amount of deposits in the geosyncline by being constantly 

 uplifted? In this way a less important change of the ocean floor would be 

 required to produce the present configuration. 



Professor Davis asked why so small a limit as 250 or 500 miles was set for 

 the width of the Atlantic foreland of the Appalachian belt. Such a width 



