Pirsson and Washington — Geology of New Hampshire. 453 



From this No. I is I, 4, 1, 3 = liparose and No. II is II, 5, 

 1, 3, = ilmenose. While these two norms are not entitled to 

 quite the weight of that derived from the chemical analysis, 

 yet, as the modes were determined on sections of large size 

 (50x40 mm , rock surface) and from a very ]arge number of 

 measurements, a fair degree of confidence may be placed in 

 them.* Suitable compositions were assumed for the horn- 

 blende and biotite in working out the chemical composition, 

 and since their amounts are not large the error in this direc- 

 tion must be inconsiderable. Assuming this, it is evident that 

 considerable variation exists in the outer exposed portion of 

 the Belknap massif, especially in regard to the amount of 

 alferric minerals, determining the class, the amount of quartz 

 determining the order, and that of lime which determines the 

 rang. 



It is to be noted that the rock from Locke's Hill is from 

 near the contact, and on this account, as seen in its high silica 

 content, it is to be regarded as homologous with the siliceous 

 border facies which has been already mentioned in the geo- 

 logical description, though it differs from this texturally in 

 being much coarser-grained. 



On the other hand, the rock from the summit of Gunstock 

 may reasonably be supposed to represent a more central part of 

 the mass of magma than the specimen analyzed, which came 

 from a spot presumably much nearer the border. There is 

 thus a successive decrease in alferric minerals with an increase 

 in quartz from center to circumference. This is more fully 

 treated in another place. 



In a specimen from the top of Piper Mountain which is 

 megascopically similar to that from Gunstock, the section 

 showed the presence of a colorless diopside associated with 

 the hornblende and more or less intergrown with it. Some 

 oligoclase also appears and these minerals, as will be shown 

 later, point to a small increase in lime in the massif towards 

 the south end. Otherwise the rock is similar to that from the 

 summit of Gunstock. 



Sor?iblende-trachi-akerose (spessartite) . 



As. previously stated, the brecciated intrusive zone at the 

 west foot of Locke's Hill contains in an aplitic liparase cement 

 blocks of various rocks brought up by the ascending magma. 

 Some of these are clearly masses of the gneisses and schists, 

 some are of the Gilfordal camptonose (essexite), while some 

 are of a dense lamprophyric type. It was thought that a detailed 

 study of one of these latter would be of interest and might 



* It is probable that the orthoclase is somewhat sodic, so that the K 2 is 

 rather too high and the Na 2 too low, but to what extent is uncertain. 



