820 TEE POPULAR SCIENCE MONTHLY. 



two or three points, but in a zone having borders parallel to the Pacific 

 coast, with an average width of about thirty miles. This formation 

 arises from the fact that Central America has had three successive 

 shores, recording as many periods of least movement in the increase 

 of the Cordillera, to each of which corresponds a line of contempora- 

 neous volcanoes. The most ancient shore was of the Miocene period, 

 when a system of trachytic and basaltic eruptions took place ; then in 

 the Pliocene rose the chain of the largest number of extinct volcanoes ; 

 while in the Quaternary and modern periods appeared the line of exist- 

 ing volcanoes and of others that have since become extinct. It is ap- 

 parent, then, that the volcanic force has always been near the shore of 

 the ocean, and has moved successively from the east to the west, so as 

 to be at only a short distance froni it, as the Cordilleras in theii* pro- 

 gressive elevation carried the shore farther in that direction. These 

 views, incontestable to me, are plainly read on the strata of the country. 



The system of volcanoes is completed by a chain of lakes alternat- 

 ing with them. The principal lakes are those of Managua and of the 

 roads of Fonseca, the latter of which has been put in communication 

 with the ocean by means of some volcanic convulsion. The roads of 

 Nicoya and Chiriqui seem to me to be of the same origin. This part 

 of the system is surely one of the most remarkable aggregations of 

 lakes and volcanoes in the world, and strikingly reminds us, but on a 

 grander scale, of that of the lakes of Liraagne, Issoire, and Brassac, 

 with the chain of the jyuys of Auvergne, which would correspond with 

 the chain of the Marrabios. Starting at the roads of Fonseca, the chain 

 of lakes and volcanoes continues, the former diminishing in importance, 

 to San Salvador and Guatemala. I am not speaking of the numerous 

 picturesque crater-lakes which we meet everywhere in Central America, 

 and which I regard as an accident of no particular importance. 



A phenomenon well worthy of attention may be observed at the 

 foot of the chain of volcanoes near Ahuachapan, in San Salvador, in 

 the Ausales, some three or four hundred conical tunnels scattered 

 over a space of about three square leagues, their diameters vary- 

 ing from three or four metres to thirty or thirty-five metres, from 

 which occur, at short intervals, eruptions of vapors, boiling water, and 

 argillaceous mud of many colors. They arc grouped by dozens very 

 close together, and poison the plain with their acid and sulphurous 

 emanations. The ground around them resounds under the feet of the 

 traveler, but only along lines which seem to be immediately over the 

 subterranean channels through which the hot water and gases cir- 

 culate. 



From this multiplicity of volcanoes it results that the ground pre- 

 sents a complicated net-work of ancient and modern lava-flows, cross- 

 ing one another, volcanic alluvions, beds of cinders and tufas, " bad 

 lands," and an extraordinary thermal activity. There also follows a 

 remarkable frequency of earthquakes and subterranean noises, called 



