PATAGONIAN BASALTS 795 



Table XII 



Norm of Patagonian Basalt 



Quartz 3 . 54 



Orthoclase 3 . 89 



Albite 20.96 



Anorthite 19 . 74 



Diopside 15.44 



Hypersthene 19.20 



Magnetite 6.73 



Ilmenite 5.02 



Apatite 1 . 01 



Symbol III. "5. 3". 4 (5). 



This norm resembles closely those of most of the other plateau basalts 

 which we have studied, especially in the notable quartz (excess silica), 

 the almost equal amounts of albite and anorthite among the salic min- 

 erals and of diopside and hypersthene among the femic, and the com- 

 paratively large amounts of magnetite and ilmenite. This correspond- 

 ence with the others is concisely brought out by the symbol. 



As to the Patagonia basalts, it may be said in general, so far as we may 

 judge from the single specimen examined, that they show in their chem- 

 ical and modal features the chief characteristics of the plateau basalts. 

 We have already briefly noted that their occurrence also shews the typical 

 plateau basalt features, namely, horizontality and great extent of a series 

 of many sheets, which attain to very considerable total thickness, these 

 features indicating a state of great fluidity at the time of extrusion. 

 That they issued from fissures, at least in great part, is shown by 

 HauthaTs observations and in part by those of Hatcher. The testimony 

 of the latter, who was essentially a paleontologist and was so little inter- 

 ested in the basalts that he failed to bring back specimens, may be held 

 as of less weight than that of Hauthal, who made a special study of the 

 structural features of the whole region. 



Algonkian and Palisadan Kegions 



In order to render our survey of plateau basalts more nearly complete, 

 two regions in the United States may be mentioned; they are so well 

 known that lengthy description is uncalled for here. One of these is the 

 area of igneous rocks, of Keweenawan age, around Lake Superior.- Fol- 

 lowing a suggestion of Prof. A. C. Lane, I have named this the Algonkian 

 region. 40 The other is the long series of Triassic sills and flows which 



40 H. S. Washington : Bull. Geol. Soc. Araer., vol. 33, 1922, p. 380. 



