448 Pirsson and Washington — Geology of New Hampshire. 



Inclusions in Lassenose. — In the border facies of the mass 

 are to he seen, as noted by Hitchcock, dark inclusions or 

 schlieren of variable size. Sometimes these are angular and of 

 definite shape. Under the microscope they show the char- 

 acteristic minerals, such as quartz, brown mica, iron ore, etc., 

 and the fabric seen in certain hornfels, and are no doubt frag- 

 ments of schists, etc. caught up and metamorphosed by the 

 magma. In other cases, as in the occurrences on the slopes 

 above Point Belknap, they may have no definite form but are 

 streaks and smears through the rock. The study of them in 

 thin section reveals a type of rock closely allied to monzonase, 

 monzonites in the current nomenclature. They are corn posed 

 of a colorless to pale green pyroxene, green hornblende and 

 brown biotite, labradorite and alkalic feldspar with accessory 

 iron ore, apatite, etc. The labradorite is in stout laths which 

 serve as cores for irregular ragged masses of feldspar, the 

 plagioclase core passing outwardly into alkalic feldspar 

 mantles. Broad areas of the soda orthoclase also occur poikili- 

 tically enclosing other minerals. The amount of the ferro- 

 magnesian minerals, though variable from place to place in 

 kind, is in amount nearly equal to the feldspathic. The masses 

 in fact closely recall types from Monzoni and Togo Beak, 

 Montana. They are believed to be of magmatic and not of 

 foreign origin, and the study of the brecciated zone on the 

 west side of Locke's Hill, as described elsewhere, throws light 

 on their origin. 



Ilornblendic-grano-pulaskose (syenite). 



This is by far the most important rock in the area from the 

 geologic point of view, as it forms the major part of the great 

 massif. A certain type of it appears to be rather uniform 

 over the exposed area, although minor variations which will 

 be described occur from place to place. For purposes of 

 chemical and microscopical analysis and study a representative 

 specimen was selected from a ravine on the west slope of Mt. 

 Belknap about a third of the way from Morrill's farm house 

 to the top of the peak. 



Megascopic. — Phanerocrystalline ; medium to coarse- 

 grained ; pale reddish, white to gray ; dominantly feldspathic 

 but sparsely dotted with aiihedra of black hornblende and of 

 biotite ; of a granular to subporphyritic fabric ; feldspars 

 mostly equidimensional, occasionally larger than the average 

 and subtabular to prismatic ; fracture rather crumbly ; super- 

 ficially somewhat altered. 



Microscopic. — Alkalic feldspar and hornblende essential ; 

 biotite, iron ore, apatite, oligoclase-andesine, quartz and zircon 

 accessory. 



