ALGONKIAN AND PALISADAN REGIONS 797 



An average of eight analyses of New Jersey Palisadan basalts is given in 

 Table XIII. These basalts, both Algonkian and Palisadan, do not show 

 the very high percentages for the iron oxides which we have found in the 

 Deccan and other plateau basalts, but they would appear to be higher 

 than the average of ordinary basalts. We see in the average norm an 

 excess of silica, which is characteristic of plateau basalts, and the similar 

 approximately equal amounts of albite and anorthite, and of diopside 

 and hypersthene. 



No more than mention may be made here of the Stormberg plateau 

 basalts of the Karroo system, in South Africa. It is hoped soon to under- 

 take a study of them, in conjunction with Dr. Fred E. Wright, who has 

 recently returned from the region with many specimens. 



Table XIII 



Averages of Plateau Basalts 



1 2 3 4 5 6 



Si0 2 50.61 49.98 47.46 50.74 50.66 48.78 



AL0 3 13.58 13.74 13.89 12.60 14.28 15.85 



Fe 2 3 3.19 2.37 3.58 4.78 3.41 5.37 



FeO 9.92 11.60 9.38 7.25 8.58 6.34 



MgO 5.46 4.73 6.79 9.00 6.92 6.03 



OaO 9.45 8.21 9.83 8.90 8.60 8.91 



Na 2 2.60 2.92 2.90 2.59 2.92 3.18 



K 2 0.72 1.29 1.01 0.72 0.72 1.63 



H 2 0± 2.13 1.22 1.48 .... 2.28 1.76 



Ti0 2 1.91 2.87 2.71 2.73 1.30 1.39 



P 2 5 0.39 0.78 0.43 0.37 0.17 0.47 



MnO 0.16 0.24 0.22 0.31 0.12 0.29 



100.12 99.95 99.78 99.99 99.96 100.00 



1. Deccan basalts ; 11 analyses. 



2. Oregonian basalts ; 6 analyses. 



3. Thulean basalts ; 33 analyses. 



4. Patagonian basalt; 1 analysis. 



5. New Jersey basalts ; 8 analyses. 



6. Daly's average basalt. 



Conclusions 



CHARACTERS OF PLATEAU BASALTS 



We may now summarize the general characters of the plateau basalts. 

 Structurally, they have characteristically issued from fissures, although 

 this quiet extrusion is sometimes accompanied by minor explosive activity. 

 They form horizontal flows of very great extent, indicating a high degree 



