23 



foot 11 inches, 1 foot 10 inches, 1 foot 6 inches, and 1 foot 9 

 inches — thus giving it a circumference of 12 feet. This crystal 

 yet remains at the locality, but the quartz and feldspar sur- 

 rounding it have been carefully removed by chisels, so that its 

 position in its native bed can be readily observed. Three weeks 

 labor of two men was expended in this process, as ordinary blast- 

 ing by gunpowder would have destroyed the crystal. Its weight 

 is probably not less than five tons. 



Dr. C. T. Jackson, at tlie request of Mr. Alger, gave a descrip- 

 tion of the Geology of Alger s Bertjl Hill, in Grafton, N. H., 

 where the above-mentioned crystals are found. They occur in 

 a very largely crystallized vein of Granite, which traverses the 

 hill of mica slate. In extracting the crystals of beryl, large 

 quantities of orthose or potash feldspar, suitable for making the 

 finest porcelain ware, were obtained, and this is now exported to 

 England for that purpose. Plates of mica, a foot or more square, 

 are also obtained, and are useful for making windows to stove 

 doors, &;c. 



Dr. Jackson next proceeded to give an account of the Trap 

 Dykes., and of the rocks altered by fire which were observed by 

 the Society upon the coast of Cohasset, stating that the rocks 

 were originally stratified, and were of aqueous deposition, and 

 have since their deposit become metamorphosed by the agency 

 of trap rocks which underlie them and have burst through them, 

 in dykes running generally nearly east and west, with occasional 

 crossing dykes having a north and south course. The minerals 

 produced in the metamorphosed rocks, by the influence of the 

 trap, are amygdules of feldspar, invested with a thin layer of 

 Epidote, and of nodules of Epidote, like those of the Nahant 

 rocks. Boulders of quartz occur in an unaltered state, in the 

 metamorphic rocks, in considerable abundance. 



Dr. Jackson then extended his remarks to the trap rocks of 

 different ages, and explained the remarkable influence they have 

 exerted on limestones, slate-rocks, and sandstones, showing their 

 agency in producing crystallized minerals and metalliferous ores 

 of various kinds. In Nova Scotia and on Lake Superior, the 

 trappean rocks, passing through the new red sandstone strata, 

 combine with the ingredients of that rock, and also form an 

 abundance of most beautiful minerals of the Zeolite family. 



