224 GEOLOGY. 



of Silurian crystalline rocks would certainly produce a radical change 

 in the existing opinions of many geologists. It is indeed recognized 

 that fossils have been found among crystalline rocks, but since the 

 lowest formations are crystalline, and the lowest of all are gneisses, 

 in the absence of fossils among such rocks they have been called 

 Archaean. This has been much to the convenience of the geologists 

 and much to the benefit of system. Geologists are slow to change their 

 convictions, therefore, on this point, because also some crystalline schists 

 of claimed modern age, as, for 'example, among the Alps, have been 

 proved to be not so. The unaided work of Professor Dana must be 

 considered as an important contribution to the literature of this subject, 

 as also to jSTew England and IS^ew York geology. One can not but be 

 struck by the fact that while the stratigraphy of the fossiliferous forma- 

 tions of Xew York were worked out in such a masterly manner as to 

 give the nomenclature to American geology, the crystalline formations, 

 both as regards their lithology and their stratigraphy, were left as a 

 comxjletely unsolved riddle. 



VOLCANIC PHENOMENA. 



The violent eruption of Mount Etna has been the most important 

 volcanic event of the year. This is not because it was so especially 

 grand or remarkable, but Etna and Vesuvius have been longer and 

 more critically studied than any volcanoes on the earth; and conse- 

 quently every minor event connected with these volcanoes, situated so 

 near centres of scientific learning, is very important, while an eruption 

 of any volcano in distant lands is less interesting only because less 

 studied. When early in May, 1879, it was announced that Etna was in 

 eruption, hours had not elapsed before eminent scientists were en route 

 from all parts of Europe. The lavas were not cold before they were 

 analyzed and microscopically examined ; and the number of independent 

 works which have followed one another, treating of the phenomena and 

 products of this eruption, has been so large as to show tbe acute 

 expectation with which the operations of this great volcano are watched. 

 The material erupted formed very large lava streams, which crystallized 

 into an augite andesite. Professor von Lasaulx, of Kiel, has recently 

 edited the extensive work of Sartorius von Waltershausen on Etna, 

 and has completed it and added numerous observations of his own. 



Vesuvius has also had its eruption, and this has strengthened the 

 opinion of some who think that there is some connection between this 

 volcano and Etna. Mauna Loa has also had a grand erui)tion, and the 

 volcanic glasses of the Hawaiian Islands have been studied by Cohen. 

 But perhaps the most interesting eruption has occurred near us, and 

 has been described by Mr. Goodyear and by a commission sent out by 

 the Government of Guatemala. In December, 1879, an earthquake 

 occurred at San Salvador which filled the earth with cracks, broke the 

 telegraph wires, shook down hills, produced great land slides, and opened 



