Pirsson and Washington — Geology of New Hampshire. 457 



The texture cannot be very well described in one word ; it 

 approaches roughly to the trachytic ; but is not porphyritic. 

 The mode on account of the large amount of hornblende is 

 abnormative and thus the rock is a hornblende-trachi-akerose. 



In Rosenbusch's system of classification the rock belongs 

 in the vogesite-odinite series of lamprophyres and corresponds 

 in general with the spessartite of this group ; the hornblende 

 is, however, not brown but common green and the considerable 

 quantity of alkalic feldspar shows relations to the vogesites in 

 which this mineral dominates the plagioclase feldspars. 



Mt. Belknap Dike. — A rock which is practically the same 

 as that just described forms a dike, six feet in width, which 

 cuts the top of Mt. Belknap with an east and west trend. It 

 differs in that it contains numerous phenocrysts of labradorite 

 with tabular development, 0'5 mm long by 0'l mm broad on the 

 average, which are quite thickly sprinkled through the dark 

 gray groundmass. The latter in thin section is similar to the 

 type just described, without however the suggestion of the 

 horn f els texture. 



It may be also noted here that the above rocks mineralogi- 

 cally are quite similar to certain facies of the grano-camptonose 

 (essexite) mass in which the latter passes locally into a monzo- 

 nose (monzonite) phase. They differ of course texturally and 

 they do not contain so much biotite, but the relation is a sig- 

 nificant one for the explanation of the origin of these dikes, as 

 will be mentioned later. 



[To be continued.] 



