Penny Blood: Serial Sensation and Working-Class Entertainment — page 270: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

cu. xx.] SEQUENCE OF VOLCANIC ROOKS. 253 have taken place at a greater distance from the mountain range, than those of a more acid character’. The “Natural System of Volcanic Rocks,” established by Richthofen and confirmed by Captain Dutton* and other geologists, appears to be explicable upon the principles we have been now advocating. Richthofen defines the volcanic era, as that which came in towards the close of the Eocene period, and extends to the present day. This period includes the epoch of the chief elevatory efforts, which have affected the greater mountain chains of both hemispheres. He classes the eruptive rocks of this era under five orders, which are (1) Rbhyolite iv, (2) Trachyte in, (3) Propylite i, (4) Andesite ui, (5) Basalt v. These are arranged in order of the proportion. of silica which they contain. But their order of successive eruption in regard to time 1s different, and is (1) Propylite 3, (ii) Andesite 4, Gu) Trachyte 2, (iv) Rhyolite 1, (v) Basalt 5. Thus the first erupted were the rocks intermediate in respect of their acidity and specific gravity, (1) and (ii). These were followed, according to Richthofen, by those of greater acidity and less specific gravity (ili) and (iv); and later by those of | least acidity and greatest specific gravity (v). This order of succession appears inexplicable on the simple theory of fluid 1 Richthofen says that Andesite occurs on the southern slope of the Carpa- thians, p. 25; and that Basalt occurs in the neighbourhood of the more ancient voleanic rocks (among which he classes Andesite), accompanying their ranges at some distance, itself forming extensive ranges: p. 27. Putting these state- ments together, it appears that the basaltic range is distant from the moun- tains. : 2 « Geology of the High Plateaus of Utah,” Chaps. Iv., v. COLA @ NOO (CO)