Pirsson and Washington — Geology of Peal Hill, iV. II. 433 



Akt. XLI. — Contributions to the Geology of JVevj Hamp- 

 shire: No. Ill, On lied Mill, Moultonboro ; by L. V . 

 Piksson ; with Analyses by H. S. Washington. 

 [Continued from p. 276.] 

 Petrography of the Pikes. 



The previous part of this paper deals with the geology of 

 fled Hill and the petrography of the main mass of nephelite- 

 syenite composing it. The petrography of the rocks occurring 

 in dikes in and about it will next be considered and in conclu- 

 sion some general considerations regarding the origin of the 

 rocks is given. 



Trachiphyro-miaskose {Nephelite-syenite-porphyry). 



This rock was not found in place but occurs in blocks in the 

 central western valley. The best place to find them is in the 

 stone walls of the Home farm ; they are very uncommon, 

 indicating a restricted amount of the rock. A similar type is 

 also seen in small scattered fragments on the north peak but 

 was also not found in place ; it is denser and more felsitic 

 than that in the valley below and the pieces observed are 

 deeply weathered to a red-brown color and too much altered 

 for investigation. Although not found in place the characters 

 of the rock, combined with the facts mentioned, point quite 

 clearly to its occurrence in dikes whose exposures in the main 

 rock mass are hidden under the soil and vegetation covering 

 it. As few porphyries of Brogger's aschistic class of the 

 lenfelic rocks have been described it is of interest to add a 

 new occurrence. 



Megascovic characters. — Holocrystalline ; medium dark 

 gray ; very fine but still megagranular ; of a porphyritic tex- 

 ture, rather thickly dotted with phenocrysts of feldspar of a 

 grayish white and very thin tabular on 010 and columnar on a, 

 presenting lath sections averaging 5-10 mm long by l mm broad. 

 Occasional specks of a ferromagnesian mineral. Quite fresh ; 

 of a rough hackly fracture and weathering on exposed sur- 

 faces to a yellow brown clay. 



Microscopic characters. — The following minerals are found 

 in the section ; iron ore, apatite, zircon, rosenbuschite, biotite, 

 aegirite-augite, alkalic feldspars, nephelite, sodalite and can- 

 crinite. 



The iron ore is very rare, a few grains 0'03-0*05 mm diameter 

 were observed. Zircon is not uncommon as an accessory in 

 minute grains. Apatite is seen in small occasional prismoids. 

 The biotite is of a greenish variety, a and b strong olive-green, 



Am. Jour. Sol— Fourth Series, Vol. XXIII. No. 138.— June, 1907. 

 30 



