Pirsson and Washington — Geology of Red Hill, N. H. 261 



from the west across Lake Asquam. To the left is seen the 

 north spur which extends towards Sandwich, on the right the 

 lower south peak and between it and the higher north peak 

 which forms the center of the view is the low cut saddle men- 

 tioned above. 



General Geology. — In its broad features Red Hill may be 

 described as a mass of intrusive nephelite syenite which has 

 broken up through granitic gneisses which enclose it on all 

 sides. The form and mode of intrusion cannot now be 

 definitely determined, but from certain considerations which 

 will presently be given, it appears probable that the mass was 

 of the nature of an intruded stock whose dome-like upper sur- 

 face solidified beneath a heavy cover. Following this came 

 secondary intrusions of magmas, on the one hand more silice- 

 ous and on the other more ferro-magnesian than the main 

 mass, which appeared as dikes both in the nephelite syenite it- 

 self and radiating outward from it in the cracked and shattered 

 gneisses. Since then erosive agencies have removed an enor- 

 mous but unknown amount of material, cutting away all of the 

 cover and the surrounding gneisses and leaving the syenite, on 

 account of its superior resisting qualities, projecting as it now 

 does above the general level of the enclosing rocks. It has, 

 however, been also bitten into by erosion, which has given it 

 its present contours, though it seems probable, as will be 

 shown later, that no relatively great amount of it has been 

 carried away. 



And lastly during the Glacial Period it was over-ridden by 

 the ice sheet as shown by the polishing and scoring of its upper 

 surfaces and by the number of erratic bowlders coming from 

 more northerly sources in the White Mountains which lie 

 scattered upon its top and upper slopes. 



The enclosing Gneiss. — No special study has been made of 

 the gneiss through which the syenite has been intruded. On 

 the geologic map of the Hitchcock survey it appears as the 

 " Winnepesaukee Gneiss." It has been observed at several 

 places, however, and sections cut from these and consideration 

 of the specimens show that it is an ordinary granitic gneiss 

 consisting chiefly of orthoclase and quartz with considerable 

 oligoclase and variable amounts of biotite and muscovite. In 

 some places it is of medium coarseness of grain, in others much 

 finer and with diminished amounts of biotite it assumes an 

 aplitic facies. Its minerals exhibit clearly the effect of 

 dynamic stresses, the quartz is strained, broken and shows 

 undulatory extinction, the twinning lamellge of the oligoclase 

 are also bent, curved and faulted, and both it and the ortho- 

 clase show at times some undulatory extinction. The mortar 

 structure is also quite pronounced. The biotite, though 



Am. Jour. Sci.— Fourth Series, Yol. XXIII. No. 136.— April, 1907. 

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