The Mont ere gi an Hills. 



229 



somewhat larger proportion of lime as compared with the 

 alkalies. 



The proportions of the several minerals present in thin 

 sections of the specimens analyzed were then determined 

 by the system of diametral measurements proposed by 

 Eosiwal. 1 In each case over 500 average diameters were 

 measured instead of 100, which latter number Eosiwal 

 considers to be sufficient. The measurements were, how- 

 ever, confined to a small number of thin setions, namely 

 two in the case of No: 1, and four in the case of No. 2, it 

 being considered advisable to use only sections cut from 

 the actual specimen from which the material for analysis 

 was taken The results obtained were as follows : 



Feldspar. . 

 Nepheline . 

 Pyroxene. . 

 Hornblende 

 Biotite .... 

 Olivine .... 

 Iron Ore. . . 

 Apatite. . . . 



No. 1 



63.77 



per cent. 



64.06 



per cent. 



6.12 



" 



6.16 



" 



9.26 



(C 



13.60 



" 



8.06 



( ( 



1.29 



<< 



2 11 



" 



4.07 

 1.40 



a 



8.56 



<f 



8.10 



Y 



2.12 



" 



1.29 



" 



100.00 



No. 2 



99.97 



In the case of No. 1 the results are substanially the 

 same as the calculated mode except that there is about 3 

 per cent, more pyroxene and a correspondingly smaller 

 proportion of feldspar. This relatively high proportion 

 of pyroxene is unusual, the examination of thin sections 

 of the rock for various, parts of the mountain showing 

 that, as has been stated above, and as is shown also by 

 the calculation of the mode of this specimen, there is 

 usually a preponderance of hornblende over pyroxene. 

 In the case of No. 2 the chief difference between the 

 values measured and the calculated mode lies in the rela- 

 tively higher proportion of feldspar and lower proportion 



1 Vtrhd. K. K. Geol. Reichsanst. (Wien, 1898), p. 143. 



