1864.] T. STERRY HUNT ON LITHOLOGY. 167 



cral species are small brilliant crystals of yellowish sphene, and 

 others of magnetic iron, amounting together probably to one thou- 

 sandth of the mass. In some finer-grained varieties a few rare 

 crystals of sodalite and of nepheline are met with. But for the 

 uniform absence of quartz, these rocks might be taken for varieties 

 ■of granite and syenite. They are very friable, and subject to 

 disintegration, so that the soil for some distance around these 

 mountains is almost entirely made up of the separated crystals of 

 feldspar ; which however show but little tendency to decomposition, 

 and retain their lustre. The rock is sometimes rather finely granu- 

 lar in its texture ; but is often composed of cleavable masses of ortho- 

 clase, which are from one fifth to one half of an inch in breadth, 

 and sometimes nearly an inch in length. The lustre is vitreous, and 

 in the more opaque varieties, pearly ; but the crystals never exhibit 

 the eminently glassy lustre nor the fissured appearance that 

 characterizes the feldspars of many European trachytes which are 

 similar to them in composition. The color of the feldspar of these 

 rocks is white, passing into reddish on the one hand, and into pearl- 

 gray or lavender-gray on the other. 



Specimens of the rock of Brome Mountain were taken from the 

 side near to the village of West Shefford. It was coarsely crys- 

 talline, lavender-gray in color, and contained a little brown mica, 

 sphene, and magnetic iron, but no hornblende. The density of frag- 

 ments of the rock was found to be 2.632-2.638. Selected grains 

 of the feldspar had a specific gravity of 2.575, and gave by analy- 

 sis the result ii. The analysis of a second specimen from another 

 portion of the hill, is given under ill. 



The rock from the south side of Shefford Mountain was next 

 examined. In one part it consisted of a coarse-grained grayish- 

 white feldspar with a little black mica, and closely resembled the 

 rock just described from the adjacent mountain. A little lower 

 down the hill however was a variety which, though completely 

 crystalline, was more coherent and finer-grained than that of Brome, 

 the feldspar rarely exhibiting cleavage-planes more than a fourth 

 of an inch in length. Brilliant crystalline grains of black horn- 

 blende about the size of grains of rice were sparingly disseminated 

 through the mass, together with very small portions of magnetite and 

 yellowish sphene. Fragments of the rock had a density of 2.6 07- 

 .2.657. The feldspar was yellowish- white and sub-translucent, with 

 a somewhat pearly lustre. By crushing and washing the mass, the 



