﻿26 A. Hague and J. P. Iddings — Volcanic Rocks 



Art. IV. — Notes on the Volcanic Bocks of the Republic of Sal- 

 vador, Central America ; by Arnold Hague and Joseph 

 P. Iddings, of the U. S. Geological Survey. 



Mr. W. A. Goodyear, for a long time in the employ of 

 the government of the Kepublic of Salvador, Central America, 

 as mining engineer and geologist, has recently sent us for 

 examination and comparison a small but interesting collection 

 of volcanic rocks, gathered by himself in the course of his 

 explorations in that country. 



Salvador is the smallest of the Central American Republics. 

 It stretches along the shore of the Pacific from the Gulf of Fon- 

 seca to the border of Guatemala. Fifteen miles inland from 

 the coast the mountains rise abruptly above the plain, present- 

 ing a chain of volcanoes at irregular intervals with a trend 

 about north-78°-west approximately parallel with the ocean. 

 The principal volcanoes in the republic are Apaneca, Izalco, 

 San Salvador, Santa Ana, San Vicente, San Miguel, and 

 Tecapa. None of them reach any great altitude above sea- 

 level, but many have been more or less active within historic 

 times, while the now famous volcano of Izalco has been wholly 

 built up since the occupation of the country by Europeans. 

 Between these isolated cones and to the northward stretch 

 broad table-lands largely made up of volcanic materials cut 

 through by streams running to the ocean. The broad, general 

 features of these volcanoes and their relations to the phj^sical 

 geography of Salvador, have been described with some detail 

 by travelers who have from time to time explored the country. 

 Notably among these may be mentioned geologists Dollfus 

 and Mont-Serrat, who visited Central America by order of the 

 French government in 1864, and published upon their return, 

 in an elaborate volume, the results of their expedition.* 



The vast accumulation of volcanic rocks, lavas, pumices and 

 ashes poured out in Central America appear to have been very 

 little investigated by modern methods of research. A few 

 notes, therefore, which we are able to offer may not be without 

 value to those interested in the lithology of volcanic eruptions. 



The specimens collected represent recent volcanic flows, the 

 summits of craters, the slopes of the more important volcanoes, 

 the bottom of deep canons, table lands, mining districts and 

 quarries. While the collection contains no suite from any one 

 locality showing the relations between different varieties of 

 rocks, it is sufficiently full to be considered as typical of the 

 eruptive rocks of the country. 



* Voyage dans Guatemala et Salvador. Paris, 1868. 



