84 



GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



upheaved by frost, is a very striking object, suggesting- immediately the 

 idea of igneous action. 



I visited the place once when, after heavy rains, the fine brook which 

 runs down from the high ground in a great gorge lined with bowlders of 

 the weathered serpentine, and the succession of beautiful waterfalls, derived 

 a peculiar charm from their setting in the warm browns and greens of the 

 rugged serpentine masses. 



The serj^entine locally is rich in chromite, and a considerable excava- 

 tion made in mining for it exists in the woods near the southeast extremity 

 of the bed. Small veins of precious serpentine, much jiicrolite, and crusts of 

 hydromagnesite of some thickness occur. It also furnished to Dr. Emmons 

 the well-known pseudomorphs of serpentine after chrysolite, formerly called 

 serpentine after quartz, or hampshirite, the exact locality of which l have not 

 been able to recover,^ and was doubtless the origin of the large masses of 

 yellow chalcedony found in Chester by the same geologist. These pseudo- 

 morphs are large, distinct crystals more than an inch long. They are six- 

 sided prisms terminated by six faces which have some resemblance to the 

 ending of a quai*tz crystal, in which two opposite faces predominate, but 

 giving the angles of chrysolite. They are covered by a straw-yellow, 

 secondary serpentine of a compact but slightly radiate-fibrous structure 

 (picrosmine) ; it is homogeneous and almost apolar under the microscope. 

 An analysis was made for me by Miss Helen P. Cook, of the chemical 

 department in Smith College. 



Analysis of pseudomorphs of serpentine. 



SiOj 



Per cent. 

 40.27 



MgO 40.00 



4.74 

 0.92 

 13.38 



FejOr, [AI2O3 trace] 



Ignition, 6+ hours, 55° to 150° C. 

 Ignition, open flame and blast . . 



99.31 



Secondary shrinkage joints in serpentine. — The detached blocks of the 

 serpentine have often suffered secondary decomposition, so common with 



' These are fully described and figured, and the proof of their derivation from chrysolite is given, in 

 A mineralogical lexicon: Bull. U. S. Geol. Survey No. 126, 1895, pp. 92, 146, under "Hampshirite." 



