1878.] 311 [Wadsworth. 



larger and better crystallized than in the feldspar, but are not as 

 numerous. The finer bands in the Quincy syenite are made up of 

 intimate mixtures of quartz, orthoclase, and plagioclase, holding 

 flocculent hornblende. 



The statements made regarding the mineral composition of the 

 Rockport stone differ in the various papers which touch upon this 

 subject. For instance, President Hitchcock wrote 1 : — "Sienite: 

 Feldspar, Quartz, and Hornblende. This variety embraces nearly all 

 the sienite in the state that is employed for architectural purposes, 

 including the quarries at Quincy and those on Cape Ann. Feldspar 

 is the most abundant ingredient. This is foliated, and commonly of 

 a grayish, bluish, or yellowish color. A hyaline quartz, varying in 

 color from quite light to quite dark gray, is very uniformly mixed 

 with the feldspar, so as to exhibit homogeneousness in the midst of 

 variety. In general, the hornblende, which is black, is very sparingly 

 disseminated, and hand specimens often contain not a particle. 

 Indeed, over extensive tracts I have sometimes not met with any." 



Rev. Stillman Barden, speaking of Rockport, 2 says: — "This is a 

 region of hard, stern granite; unpoetical, perhaps, but full of inter- 

 est to the mineralogist. The rock seems like sienite, from the very 

 dark hue of the mica, but is yet a true granite with all the value of 

 that eldest of all the rocks." Again he says 3 : — "In the extensive 

 quarries worked by Fames and Co., can be seen some of the best and 

 purest granite in the country; there is almost an entire absence of 

 hornblende. Granite contains quartz, feldspar and mica — sienite, 

 quartz, feldspar and hornblende; frequently the four ingredients are 

 found combined together, viz.: quartz, feldspar, mica and hornblende; 

 hence the rock of this region may be termed sienitic granite." 



Professor J. P. Cooke writes 4 : " The mica which is associated 

 with cryophyllite at Rockport (or as we should rather say, with 

 which cryophyllite is associated, for cryophyllite is the subordinate 

 species), is an iron mica of the species lepidomelane. This is the 

 common mica of the great granite ledges which form the extremity 

 of Cape Ann. In the granite itself, however, it occurs only in small 

 flakes, forming a very small proportion of the whole mass ; but in the 

 numerous veins which intersect the rock, lepidomelane is found in 



1 Geology of Massachusetts, Final Report. 1841, page 668. 



2 Proceedings of the Essex Institute, 1802, Vol. in, page 205. 



3 Proceedings of the Essex Institnte, 1863, Vol. in, page 231. 



« American Journal of Science, n Ser., Vol. xliii, 1867, page 222. 



