GEOLOGICAL AND MINERALOGICAL NOTES. 187 



No. 48. Opal, var. Tripolite : Infusorial Earth. 



Found in beds of brooks and meadows in Danvers. At 

 West Boxford beds occur two feet or more in thickness. 

 No. 49. Hypersthene. 



In irregulär, cleavable, crystalline grains and masses 

 in the hypersthene-gabbro at Misery Island and Salem 

 Neck. 

 No. 50. Wollastonite : Tabular Spar. 



A bladed variety of this mineral is found at the Devil's 

 Den, Newbury. 

 No. 51. Diallage. 



Found in large crystalline masses at the Luther Noyes 

 nickel mine, Newbury. 

 No. 52. Pyroxene, var. Augite. 



In irregulär crystals in the augite-nepheline-syenite at 

 Salem Neck, Beverly and Manchester. 

 No. 53. Diopside, var. Brown Augite. 



This occurs as irregulär, microscopic crystals in the 

 augite-nepheline-syenite on the Pickman estate, Beverly 

 Cove. 

 No. 54. Acmite. 



This occurs as small acicular crystals in the augite- 

 syenite at Powder House hill in Essex, and at Lanesville 

 in Gloucester. 

 No. 55. iEgirine. 



Typical bent crystals, sometimes three inches long, are 

 found in the regirine-syenite at Gale's Point, Manchester. 

 (Sears Bull. Essex Institute, Vol. xxiii, Min. and Geol. 

 Notes, No. 3, p. 5.). It is also seen in thin sections of the 

 elseolite-zircon-syenite of Salem Neck and Beverly when 

 studied with the microscope. 

 No. 56. Enstatite. 



In micro-crystals in the olivine-gabbro of Salem Neck. 

 No. 57. Bronzite. 



