BUILDING AND ORNAMENTAL STONES. 431 



coarse, and the contrast of colors such that one can scarcely imagine 

 a more beautiful stone for rock-faced work. It is very tough, and, to 

 judge from the bowlders, is also very durable, and not at all liable to 

 discoloration on exposure. 



Hawes* describes augite syenites as occurring in Jackson, Columbia, 

 and on Little Ascuntney Mountain, in New Hampshire; also hornblende 

 syenites as occurring at Red Hill and Moultonborough, Columbia, Sand- 

 wich, Stark, and Albany, in the same State. Dr. Wadswortht also 

 mentions a syenite as occurring in eastern Massachusetts, where it oc- 

 cupies a large proportion of the coast line between Salem and Man- 

 chester. None of these are as yet quarried. 



Near Hot Springs, in Arkansas, there is quarried under the name of 

 granite a tough gray rock of variable texture, consisting mainly of horn- 

 blende and elreolite, and which would therefore be classed as an ehneolite 

 syenite. Some portions of the rock, as shown by the large block in the 

 Museum collection, are fine-grained and homogeneous, while in others 

 the eloeolite crystals reach some 2 or 3 inches in length. The appear- 

 ance of the stone is excellent, but portions of it contain a large amount 

 of pyrite and it needs to be selected with care if designed for exterior 

 or highly ornamental work. 



A syenitic rock bearing abundant elasolite and frequently cancrinite 

 and sodalite, and which must, therefore, also be classed as an elceolite sye- 

 nite occurs abundantly in the vicinity of Litchfield, Me., and specimens 

 of the rock have found their way into the building-stone collections of 

 the Museum. An examination of the rock does not, however, impress 

 one particularly in its favor. Its durability is, to say the least, doubtful, 

 and its varying texture and colors rather against it. 



(3) THE TRACHYTES AND PHONOLITES. 



Under the name of trachytes are comprehended by Eosenbusch those 

 massive Tertiary and post Tertiary rocks consisting essentially of san- 

 idin and hornblende, augite or black mica, and which may be regarded 

 as the younger equivalents of the syenites and quartz free porphyries. 



The average chemical composition is silica, 63.55; alumina, 18.0; iron 

 oxide, G.15 ; lime, 1.96 ; magnesia, 0.88 ; specific gravity, 2.65. 



In structure trachytes are rarely granular but usually possess a fine 

 scaly or micro-felsitic groundmass, rendered porphyritic by the devel- 

 opment of scattering crystals of sanidin, hornblende, augite, or black 

 mica. The texture is porous and possesses a characteristic roughness 

 to the touch ; hence its name from the Greek word rpayo- rough. The 

 prevailing colors are gray, yellowish or reddish. 



Trachytes are volcanic rocks occurring in eruptive masses in dikes 

 and in lava flows. They may be divided into hornblende, biotite, or 



*Geol. of New Hampshire, Vol. in, Part IV, p. 205. 

 tGcol. Mag., May, 1885, p. 207. 



