510 Reviews — Richthofen^s System of Volcanic Rocks. 



I. — The Natural System of Volcanic Eocks. By F. Bakon 

 EiCHTHOFEN, Dr. Phil. Printed by the California Academy of 

 Sciences, San Francisco, 1868. 



IN a notice of the work of two French geologists on Central 

 America in the last number of this Magazine, regret was ex- 

 pressed that imperfect ideas upon volcanic action had prevented 

 their just appreciation and clear description of the geology of that 

 district ; especially of the great development of Trachytic rocks 

 observable there. The same remark applies to the work named at 

 the head of this paper by a German geologist, who, possessing the 

 advantage of a previous acquaintance with the volcanic regions of 

 Germany and Hungary, recently visited the North-west coast of 

 America, and has dealt with the subject of volcanic rocks in an 

 elaborate memoir presented to the California Academy of Sciences, 

 and printed by them at San Francisco in 1868. 



The value of M. Eichthofen's "Natural System of Volcanic 

 Eocks," as a contribution to the science of geology, maybe estimated 

 from the fact that he denies the occurrence of any volcanic rocks in 

 the series of geological formations preceding the commencement of 

 the Tertiary Era. (What will Sir Eoderick Murchison, Professor 

 Eamsay, or Mr. A. Geikie say to this ?) And his " System of 

 Volcanic Eocks " is divided into two great classes ; the first and 

 earliest that of " Massive Eruptions," which, though " volcanic," 

 were " not produced by volcanos" ; the second, and latest in time, the 

 products of " Volcanos proper." M. Eichthofen goes on to divide 

 each of these two classes of rocks into five " orders," determined by 

 their mineral characters, called by him respectively, 1. " Propylite " 

 (Greenstone — Trachyte, or Greystone — i.e., a Trachyte in which 

 Hornblende or Augite occurs in noticeable quantity) ; 2. Andesite 

 (a mere variety of the latter rock) ; 3. Trachyte proper ; 4. Ehyolite 

 (Siliceous Trachyte, Pearlstone, and Obsidian) ; 5th. Basalt. These 

 difierent kinds of volcanic rock succeed one another, according to M. 

 Eichthofen, "invariably over all the globe," in the sequence here 

 given, not once only, but twice over, that is, in each " class ;" — in the 

 earlier period of "massive eruptions," and in the later period of 

 "volcanos proper." 



It is needless to say that these arbitrary classifications and as- 

 sertions as to the relative age of particular varieties of volcanic 

 rocks are wholly at variance with known facts, and the authority of 

 the most reliable observers of such formations. 



The epithet " massive," applied by M. Eichthofen to his class of 

 earlier volcanic rocks, would seem to indicate some distinction 

 founded on the vastness of the scale on which they occur, as com- 

 pared with the " volcanic rocks proper." But see the following de- 

 scription by him of an admitted " volcano," Lassen's Peak, in 

 Northern California (p. 33). 



" The enormous hidJc of this ancient volcano is totally built up of 



