DYNAMICAL GEOLOGY. 2/5 



of Guatemala and San Salvador were described in 1868 by 

 M. Dollfuss-Montserrat, and Dr. Sapper has recently been 

 engaged on a series of researches in this area. 



There have been comparatively few geological publications 

 dealing with the volcanoes and volcanic rocks of South 

 America since the pioneer works of Humboldt. Dr. Alphons 

 Stiibel has, however, made a special study of the volcanic 

 mountains of Ecuador, and published in Berlin in 1897 a 

 special monograph of the district, accompanied by a Geo- 

 logical Map. Dr. Stiibel gives a summary of his results in 

 the introductory chapter, where he represents his views on 

 volcanic phenomena from a general standpoint. He thinks 

 it probable that in the first stage of the Earth's cooling, out- 

 pourings of magma occurred so frequently, and were of such 

 colossal dimensions that the older volcanic material had only 

 partially solidified when younger outflows burst forth and 

 spread above them. In this way the cooling of the older 

 magmas was indefinitely delayed, and they continued as local 

 "peripheral" cisterns or reservoirs of volcanic material, occur- 

 ring at very small depths below the surface, and extremely 

 sensitive to any variation in the surrounding physical con- 

 ditions. Dr. Stiibel regards these "peripheral" reservoirs 

 as the base of supply from which present volcanoes derive 

 their volcanic material, and he correlates the surface extent of 

 volcanic groups and the arrangement of the individual erup- 

 tive vents or fissures with the original shape and size of the 

 respective areas of primitive, uncooled magma. The force 

 which enables it to rise again to the surface resides, according 

 to Dr. Stiibel, in the magma itself, and the region of the least 

 resistance is the path along which the liquid masses find their 

 way to the surface. The conditions of least resistance, he 

 adds, are most commonly met with at the limits of different 

 kinds of rock. 



The scientific study of the extinct volcanoes, and especially 

 the exact petrographical examination of the products of erup- 

 tion, has exerted a marked influence on the theoretical 

 explanation of volcanic phenomena. It was only to be ex- 

 pected that exact knowledge should finally dispose of many 

 fanciful hypotheses, such as those which explained volcanic 

 action from the burning of coal-seams or petroleum, the 

 decomposition of sulphur metals and other substances, from 

 electricity, or the local disengagement of vapours. 



