Pirsson and Washington — Geology of Red Hill, N. H. 443 



described elsewhere, has some zircon ; it also has considerable 

 titanite. 



Phyro-nordmarhase {Syenite-porphyry) . 



It has been stated in the geological part of this work that a 

 dike of feldspar porphyry occurs on Fore Point, and that frag- 

 ments of a similar rock are found on the north peak of Red 

 Hill. They are too much weathered for detailed study and 

 analysis, but from the material and the section of the Fore 

 Point rock the following has been determined : 



Megascopic. — Holocrystalline ; dense and porphyritic ; brown- 

 gray weathering to red-brown ; thickly sowed with white to 

 flesh- colored feldspar phenocrysts, thick tabular in form and 

 2-5 mm across and with scarce, dull, greenish black, altered 

 ferromagnesian phenocrysts averaging 2-3 mm long by - 5 mm 

 broad. Rough, hackly fracture, much jointed. 



Microscopic. — The rock consists for much the greater part 

 of alkalic feldspar which is turbid and brown with kaolin 

 granules. The phenocrysts are of microperthite, and the 

 small feldspars of the groundmass are also mixtures of ortho- 

 clase and albite. Scattered through the rock are small shreds, 

 leaves and strips of chlorite and serpentine which are occa- 

 sionally lumped together and are remains of the larger pheno- 

 crysts. They may have been mica or hornblende or both ; it 

 cannot now be told. The feldspars of the groundmass average 

 about 0-06 X O02 mra and are short broad laths. A little quartz 

 occurs now and then in their interstices. In texture the pat- 

 tern of the fabric from these feldspars is trachytoid with a 

 tendency to the granular. 



Classification. — The rock is clearly persalic, perfelic and 

 peralkalic ; its coordinates are I, 5, 1, and it is therefore nord- 

 markase. If we assume that there is about an equal amount 

 of orthoclase and albite present as indicated by the section and 

 in analogy with the other rocks of the district, it would be 

 sodipotassic and in subrang 3. Taking the texture into 

 account it would then be trachiphyro-phlegrose. 



In the system of Rosenbusch the rock is a syenite-porphyry ; 

 its mode of occurrence and character of groundmass would make 

 it a bostonite, especially if one considers its genetic relations. 

 It would then be a bostonite porphyry. 



Trachi-nordmarkase (Bostonite) . 



On the south point of Hoag's Island, which forms the north 

 bank 'of the narrow strait in Lake Asquam which leads into 

 Bear Cove, the gneiss is cut by a narrow dike of feldspar rock, 

 three feet wide, with trend to Red Hill. The outcrop lies at 



