Reviews — Clarence King — Survey of Fortieth Parallel. 471 



"During the Quaternary period most modern mountain topo- 

 graphy received its present form. Most, if not all, of the sharp 

 canons were carved, and the mechanical results of that erosion are 

 seen in the great accumulations of subaerial gravel in regions of 

 interior drainage like the Great Basin, and in deposits of unknown 

 thickness classed as Lower Quaternary, which gathered on the beds 

 of the Quaternary lakes." 



It has therefore been the object of Mr. King in Chapters II. to V. 

 to give a general account of such facts as seemed to be necessary to 

 a comprehension of the sequences and subdivisions of sedimentary 

 geology. In the 120,000 feet of these accumulations, the grander 

 divisions of the Archaean or Azoic, Paleeozoic, Mesozoic, are distinctly 

 outlined by divisional periods of marked unconformity. From the 

 first of the Cambrian age to the present day every important interval 

 of time is recorded in the abundant gathering of sediments, which 

 are with singular fullness characterized by appropriate and typical 

 life forms. Of the 77,000 feet of beds from the Lower Cambrian to 

 the close of the Tertiary, nearly 20,000 feet are limestone, the rest 

 is purely detrital, the limestones, however, throughout the entire 

 Cretaceous and Tertiary are all fragmentary, and are simply the 

 pulverized sediments which were washed down from the neighbouring 

 limestone formations. 



Chapter VII. comprises the more important facts accumulated 

 during the Exploration relative to the Tertiary volcanic rocks as to 

 sequence, geological dates, modes of occurrence, reciprocal relations, 

 and petrographic distinctions. The latter subject has also been fully 

 treated in the admirable and instructive memoir by Prof. Zirkel, 

 forming vol. vi. of the series. The material is classed under three 

 groups : 1st. The detailed occurrence of species ; 2nd. The relations 

 of each rock to the orographical actions which brought it to the sur- 

 face, and the succession of each species ; 3rd. The origin of igneous 

 fusion and the genesis and petrological classification of volcanic 

 rocks. 



The close of the Jurassic age was characterized in Nevada and 

 Utah by scattered eruptions of middle-age eruptive rocks, including 

 diorite, diabase, and porphyries ; with a doubtful exception, all the 

 other volcanic series are referable directly to the Tertiary. The 

 natural sequence of the volcanic rocks observed in the Fortieth 

 Parallel corroborates the previous researches of Eichthofen, which is 

 as follows : 1. Propylites ; 2. Andesites ; 3. Trachytes ; 4. Bhyolites ; 

 5. Basalts. The acidic products are enormously in excess of the 

 basic products (as shown in Map VII.), and almost equally in excess 

 of rocks of mean constitution, as the hornblende propylites, andesites 

 and trachytes. Taken as a whole, Ehyolite is the predominating 

 volcanic rock of this field, and considerably exceeds the Basalts, 

 which rank next in territorial area. These two families, at once the 

 most acidic and most basic, cover together ten times as many square 

 miles as all the rest of the volcanic series combined. 



The section on the fusion and genesis of volcanic rocks (pp. 696- 

 725), and their classification, is well worthy of the attention of those 



