Pirsson and Washington — Geology of Red Rill, JV. H. 445 



which specimens were collected, not one afforded good fresh 

 material for chemical analysis and detailed study, all being to 

 a greater or lesser extent altered. Moreover, they are so simi- 

 lar to the dikes of camptonase occurring in the Belknap Moun- 

 tains at the other end of Lake Winuepesaukee which have been 

 minutely studied and described in a recent publication by Dr. 

 Washington and the writer,* that it hardly seemed worth while 

 to repeat again for these rocks what is there given. A brief 

 summary of their more important characters may be of service 

 in case the former paper is not at hand. 



They are very dark gray to black rocks, often speckled with 

 small areas or amygdules of calcite. In one or two cases they 

 contain visible phenocrysts of labradorite. They never show 

 abundant, large, well-developed crystals of hornblende and hence 

 they are not of the modal habit of camptonose of the original 

 locality at Livermore Falls, a habit frequently seen elsewhere 

 and which we have called the hampshiral habit. Large horn- 

 blendes occasionally occur in them but the characteristic mode 

 of occurrence of this mineral is in very small and needle-like 

 crystals, just perceptible to the eye or lens and frequently giv- 

 ing a somewhat silky appearance to the rock. 



The microscope shows them to be composed of iron ore> 

 apatite, brown alkalic hornblende, labradorite and usually 

 more or less indeterminable matter of a feldspathic character, 

 usually doubly refracting. These minerals are all more or less 

 altered ; sometimes it is the hornblende and iron ore, sometimes 

 the feldspathic minerals, generally both. The study of all the 

 sections gives a good composite idea of the original fresh rocks 

 but no single occurrence corresponds. Like those found in 

 the B.elknap Mountains, some of the dikes contain also augite 

 in addition to the hornblende. 



In summation it may be said that they represent typical 

 rocks complementary to the persalic dikes (paisanite, aplite and 

 bostonite) previously described and parallel similar occurrences 

 of alkalic rock complexes found in other regions. 



Intrusion Brecoia.—\t has been mentioned that at the 

 Home farm house the nephelite-syenite encloses a mass of dark 

 colored rock filled with fragments of the syenite itself. The 

 microscopical study of this material reveals the minerals of 

 which it is composed, but throws no additional light upon its 

 origin above what may be seen by its study in the field and on 

 hand specimens. 



The finely granular dark rock which serves as a cement to 

 the inclusions under the lens is seen to be formed of an equal 

 mixture of white feldspathic and black ferro-magnesian gran- 

 ules, the latter in part biotite. It is crowded with small frag 



* Petrography of the Belknap Mts., this Journal, vol. xxii, p. 498, 1906 



