42 MINERALOGY AND LITHOLOGY. 



ore there is a considerable percentage of titanic acid. Large amounts 

 of magnetite are associated witli the hematite at Bartlett. At Swanzey 

 large crystalline masses are found in a granite vein. In Amherst, fine 

 crystals having the planes of a cube and octahedron occur ; and rhombic 

 dodecahedral crystals are also found. The crystals at this place are 

 sometimes two inches in diameter. At Winchester there is a large vein 

 that was once worked ; it is contaminated with pyrites. Other localities 

 are Berlin, Piermont, Jackson (on Thorn mountain), Lebanon, Benton, 

 and Easton, besides many smaller deposits unnecessary to mention. 

 There are, moreover, many localities in the state, on ajDproaching which 

 the magnetic needle is very strongly deflected ; and the presence of large 

 bodies of ore is suspected but not proved. 



Native lodestones are found on Gunstock mountain in Gilford. 



Magnetite is one of the most commonly occurring minerals in rocks of 

 all kinds, and offers some interesting features for microscopic study. In 

 almost all our rocks it is present either as an essential or an accessory 

 ingredient. Even in the thinnest sections of the rocks it is perfectly 

 opaque, but it is evident that, could it be made thin enough, it would be 

 translucent, since in our mica quarries at Alstead it has been found in 

 such thin films, between the layers of mica, as to be plainly transparent. 

 These films have been shown by Prof. Brush to be magnetite.* When 

 the light from below the stage is shut off, the surface of a section of 

 magnetite has a bluish metallic lustre by reflected light. As a con- 

 stituent of the rocks, it is often in wholly irregular grains, and, again, it 

 is often in minute crystals of perfect form. In our trap rocks it is quite 

 generally crystallized ; and the little crystals are often grouped together 

 in various ways, sometimes forming quite complicated figures, f The 

 magnetite in sections of these rocks is seen in little squares or triangles, 

 which are sections of octahedrons; and in more complicated right-angled 

 forms, which result from the compounding of its isometric crystals. On 

 PI. 2 are represented some of the groups of crystals as seen in the rocks. 

 Figs. 4 and 4a are from a section of the diabase at Bemis brook; 4^ and 

 4c, from the same rock at the Lincoln Flume; and 4*^ is a more delicate 

 form, which is drawn from a section of the porphyritic diabase of Con- 



* See Dana's Mineralogy , p. 150. 



t See PI. iii, in Zirkel's Basaltgesteine. 



