454 Pirsson and Washington — Geology of New Hampshire. 



shed some light on the sequence of magmatic eruptions in the 

 area, and a specimen was selected from a large angular block 

 several feet in diameter embedded in the liparase. 



Megascopic. — Phanerocrystalline ; fine-grained, too dense 

 for the individual minerals to be recognized but perceptibly 

 granular ; very dark stone gray, almost black ; tough with 

 hackly fracture. .Rare, very inconspicuous, equidimensional, 

 dull hornblende phenocrysts 0'5-l'0 mm . Speckled here and 

 there with small grains, streaks and minute veinlets of pink 

 feldspar and quartz, the grains sometimes 2-3 mm with feldspar 

 cleavage and of ragged, broken or irregular contours, evidently 

 included or injected material and not normal phenocrysts. 



Microscopic. — The section shows iron ore, apatite, horn- 

 blende, plagioclase, alkalic feldspar and quartz. 



The iron ore occurs in two forms ; as scattered grains, some- 

 what rounded, about 0'02-0 , 05 mm , and as minute spheres, 

 ovoids and rods about 0'001 mm , sprinkled through all the 

 minerals and especially the feldspar, where they are often 

 aligned into small systems. They distinctly suggested the 

 iron ores seen in contact hornstones. 



Apatite occurs in excessively minute needles in the feldspars. 

 Hornblende is of a green color, strongly pleochroic into tones 

 of pale yellow ; it includes occasional grains of iron ore and 

 some pieces have the central part blackened by separated iron 

 ore dust and needles much like those which in lavas have 

 suffered partial resorption. It is in irregular forms with a 

 tendency to columnar development. Occasional flakes of 

 biotite are sometimes associated with it. 



The plagioclase is zonally developed with the customary 

 more calcic cores and passing to alkalic feldspar mantles. It 

 shows both albite and Carlsbad twinning, but much is un- 

 twinned and distinguished from alkalic feldspar only by its 

 zonal development. The cores are of labradorite, the outer 

 portion passing into andesine. It has a somewhat columnar 

 development parallel to the a axis, but like the hornblende 

 the boundaries are irregular. 



The alkalic feldspars are similar in form to the plagioclase 

 and are not always easily distinguised from them when 

 un twinned. From the analysis it must be concluded that they 

 are very rich in soda. 



The small spots and streaks mentioned above are irregular 

 fragments of alkalic, rarely plagioclase feldspar, often much 

 filled with sericitic muscovite sometimes accompanied by 

 quartz. They are clearly exotic, included or injected material, 

 and do not belong to the rock proper. 



Mineral Composition or Mode. — By Rosiwal's method the 

 rock was measured and calculated to have the following com- 

 position : 



