512 Pirsson and Washington — Geology of New Hampshire. 



It is to be noted, however, that some of the analyses are of 

 rocks the volumes of which are very small relative to that of 

 the whole igneous massif. This applies especially to the 

 extremes, I and VIII, which are of the complementary dikes, 

 whose total volume cannot be more than 5 per cent of the 

 whole and is almost certainly considerably less than this. 

 Similarly Y I is of a rock of minor importance and of negligibly 

 small relative mass. The area of the gilfordal camptonose 

 (VII) of Locke's Hill is considerable, but its volume is 

 undoubtedly not over another 5 per cent of the whole mass. 

 That of the bordering aplitic lassenose facies (III) is undoubt- 

 edly considerably greater, though for reasons given previously 

 it was impossible to estimate its extent with accuracy. The 

 assumption that it forms about one-tenth of the complex will 

 probably be not far from the truth. 



As to the main mass of syenite we have seen that its compo- 

 sition is somewhat variable, different portions being represented 

 by II, IV and V. Of these II is of a marginal facies and 

 probably not fully representative of the whole. Analyses IV 

 and V may therefore be held to represent the chemical com- 

 position of the bulk of the Belknap massif. These resemble 

 each other in certain respects, especially in SiO„ CaO, Na,0 

 and K 2 0, but differ in the lower Al,O s and higher Fe a 9 , FeO 

 andMgOof Y, these resemblances and differences being clearly 

 expressed by their respective places in the quantitative 

 classification. Allowing equal weight to these two analyses, 

 although Y is calculated from a measured mode, we find that 

 the composition of the syenite is that given in IX. The norm 

 of this is as follows : 



Sal Fern 



Qz 1-56 ] Di 1-14 "| 



Or 37-25 I Hy__. 5-97 | 



Ab _._. 39'82 f *° y/ Mt ... 3-25 \ ]2'68 



An 8-34 J II 1-98 | 



Ap ... 0-34 j 



The main syenite falls, therefore, in the dosalane class, but 

 almost on the border of persalane and well within the limits 

 of order 5, rang 2, and subrang 3, so that it is a pulaskose- 

 monzonose, (I— II. 5.2.3). 



We may attempt to estimate the composition of the magma 

 as a whole, although the data are somewhat unsatisfactory and 

 the results necessarily only approximately correct. For this 

 purpose we may assume the relative volumes as estimated 

 above, giving as much prominence as possible to the less abun- 

 dant rocks. We shall thus estimate the volume of the syenite 

 at eight-tenths of the whole, that of the border lassenose at 

 one-tenth of the whole, that of the gilfordal camptonose at 



