89 



The columns marked B, C, D, and E resemble, in some 

 respects, the column A. The silica in B, C, and D is notice- 

 ably lower than that in A and E, and hence are slightly 

 more basic. The alumina in B and C is higher, and that 

 in E lower, than that in A and D, which are very nearly 

 the same. The ferric iron in B, C, D, and E is noticeably 

 greater than that in A, and ferrous iron is lower in E, whilst 

 it is fairly constant in A, B, C, and D. The magnesia varies 

 slightly, being lowest in C. The lime varies a little, being 

 high in A and D, and fairly consistent in B, C, and E. 

 The total alkalies are approximately constant in A, C, and 

 D, but higher in E and lower in B. The percentages of 

 titanium dioxide in B, C, D, and E are, to a small extent, 

 higher than that in A. 



It will be noticed that basalts similar to the Mount 

 Gambier type in composition occur in the Pinto Mountains, 

 Uvalde County, Texas, described by W. Cross, (i^) which is 

 quoted by Washington in the "Chemical Analyses of Igneous 

 Rocks.'' Washington also quotes an analysis of a basalt from 

 Hiinenberg, BL, Melsungen, Prussia, which also approxi- 

 mates the composition of the basalt described in this paper. 



Calculation, of tin 



; N 



orm . 







Orthoclase 



.. 16 



X 



556 



= 



890 



Albite 



.. 29 



X 



524 



= 



15-20 



Neplielite 



.. 27 



X 



284 



= 



7-67 



Anorthite 



.. 69 



X 



278 



= 



19-18 



1 



.. 98 



X 



116 



= 



11-37 



Diopside ,' 



.. 70 



X 



100 



= 



700 



1 



.. 28 



X 



132 



= 



370 



Olivine - 



.. 173 



.. 70 



X 

 X 



140 



204 



= 



12-11 



7-14 



Magnetite 



.. 9 



X 



232 



= 



2-09 



Ilmenite 



.. 25 



X 



152 



= 



380 



Apatite 



.. 4 



X 



310 



= 



1-24 



Water 









- 



062 

 10002 



(i3)B.U.S.G.S., 168, p. 61, 1900. 



