83 Prescolt's Sketch of the Geology and Mineralogy 



dark purple, containing numerous ramifications of minute veins 

 of a scarlet color, exactly resembling the minute ramifications of 

 injected blood vessels. These veins become very conspicuous 

 upon being moistened with the breath. 



Numerous pebbles, bowlders, and masses of beautiful red, 

 purple, striped, and variegated jasper are thrown upon the south 

 west shore of Nahant, between Bass Point and Crystal Beach. 

 Some of the finest specimens have been obtained from this place. 

 The locality of the bed must be beneath the ocean. 

 Sub species 4. 



Porcelanite and silicious slate, exists at the south east part of 

 Nahant, associated with argillaceous slate, argillaceous carbonate 

 of lime, &c. It occurs also in the western section of Topsfield, 

 arid eastern section of Middleton, and bowlders of it may be 

 found in the north part of Danvers. 



SPECIES 14. MICA. 



A foliated variety of black mica occurs on Salem Neck, asso- 

 ciated with feldspar and foliated hornblende. The lamina vary 

 in size from an inch in diameter to minute scales ; and when 

 associated with foliated hornblende, it is difficult for the eye to 

 distinguish one from the other. In this instance the mica seems 

 to have assumed the place of quartz, which enters largely into 

 all the compounds of hornblende and feldspar, but which in this 

 locality is entirely wanting. 



SPECIES 15. SCHORL. 



Beautiful radiated black schorl, has been found by Dr. A. 

 Nichols, on a bowlder of hornblende rock, about half a mile north 

 of the South Village in Danvers. 



SPECIES 16. FELDSPAR. 



Feldspar, exists in great abundance. It forms an essential 

 ingredient in sienite and greenstone, and occurs crystallized in 

 various species of porphyry, and associated with quartz, horn- 

 blende, epidote, &c. It is of a white, gray, brown, green and 

 red color, and of various shades. 



Large hemitrope crystals of a grey feldspar, with a pearly lus- 

 tre, occur in the trap rocks, about the middle of the south east- 

 ern shore of Little Nahant, 



