778 H. S. WASHINGTON DECCAN SALTS AND PLATEAU BASALTS 



in general, contains small and variable amounts of olivine. This is the 

 more noteworthy in view of its silica content being the highest of those 

 in the table of analyses. 



The chemical characters of the Oregonian basalts are shown by the 

 analyses in Table III. From these it will be seen that there is much 

 more variation among them than was noted in those of the Deccan and 

 no apparent division into two groups. Silica, for instance, varies from 

 45.16 to 54.50 per cent, but there is less variation among the other con- 

 stituents. In this region we find, as we did in India, that the most char- 

 acteristic feature is the very high percentage of iron oxides (except in 

 number 6), with ferrous oxide predominating strongly over ferric in all 

 of them. Some of the ferrous oxide percentages, indeed, are exception- 

 ally high for basalts. Magnesia is low in general, the augite being evi- 

 dently strongly hedenbergitic, as in the Deccan, while lime is in about 

 the usual amounts. Although soda dominates over potash, there is more 

 of the latter in the Oregonian basalts than in the Indian, and this may 

 possibly be connected with the occurrence of rhyolites. Titanium, phos- 

 phorus, and manganese are all decidedly high, except again in the Ya- 

 kima basalt, which does not seem to be representative of the region, as 

 has been thought. An incomplete analysis by Merrill of the basalt of 

 Walla Walla, Washington, shows the same general features as those more 

 completely analyzed. 15 These general characters are well shown in the 

 average (number 7), which it is instructive to compare with that of the 

 Deccan traps. 



15 W. Lindgren : TJ. S. Geological Survey, Prof. Paper 27, 1904, p. 75. The analysis is 

 as follows: Si0 2 , 47.35; A1 2 3 + Fe 2 3 , 34.38; FeO, n. d. ; MgO, 4.43; CaO, 8.27 ; Na,0, 

 2.55 ; K 2 0, 1.33 ; H 2 0, 0.95 ; Sum, 99.26. 



