456 Pirsson and Washington — Geology of JVew Hampshire. 



P a 5 of the analysis. "With these corrections the composition 

 is as stated above and it must be reasonably correct. 



Chemical Composition. — This is shown in the analysis given 

 below and it will be seen that the rock has the usaal charac- 

 ters of a lamprophyre. The most notable feature is the pre- 

 dominance of soda over potash. The rock most nearly related 

 to this one, both in magma composition and in geologic occur- 

 rence, of which we have found an account in the literature, is 

 one from Chile given in 'No. II, while another of similar 

 composition from Mexico is given in III. It should be 

 remarked here that the analysis (I) probably does not repre- 

 sent quite accurately the composition of the pure normal rock, 

 since the small included fragments of feldspar and quartz pre- 

 viously mentioned were unavoidably present to a limited 

 extent. Their influence must be very minute, but the silica, 

 alumina and alkalies are a trifle too high on that account. 



Texture. — The average grain of the rock is about 0'05 min 

 and the hornblendes and feldspars approximate quite closely 

 to this and do not vary much in size. The fabric is that com- 

 monly seen in rocks of lamprophyric character, and which 

 Eosenbusch has designated as " panidiomorphic granular " in 

 which the constituents appear of equal age, interlock with 

 one another and yet have a distinct tendency to a columnar 

 form. This fabric, however, is not clean cut and clear, as one 

 often sees it, for the hornblendes are somewhat rounded, as 

 are the ore grains, and the feldspars are irregular in outline 

 and everywhere dotted with the little spheroids and rods of 

 iron ore. Thus in plain light there is a distinct impression of 

 the hornfels fabric with its rounded grains and dots, but when 

 the nicols are crossed this disappears and the normal fabric is 

 revealed. This is of interest because it shows that the original 

 fabric has been affected to some extent by the immersion of 

 the blocks in the liparase magma, and further evidence is seen 

 in the separation of the iron ore in the hornblendes and in the 

 sericitic mica in the large feldspars previously described. 



Classification. — In the quantitative system the calculation 

 of the norm of the rock and its position are given below. 



66-23 



Sal 66*23 TT _ . 



:= s= = 2 = II, -Dosalane 



Fem 33-05 



] — — = = 0*01+5, Germanare 



I F 65 



}■ 33-05 T7- /y_|_|j fl O' Q7 



2 „?,, = — = 1'94 = 2, Monzonase 



J CaO' 50 ' 



Total 99-99 J^ ' = — = 0'21 = 4, Akerose 



NaO' 80 



Qz____ 



0-96 



Or.... 



9-45 



Ab _._ 



41-92 



An ... 



13-90 



I>i__._ 



12-33 



Hv --- 



8-11 



M 



7-45 



Mt ... 



3-48 



A P ._. 



1-G8 



Rest . . 



0-71 



