57 



Prof. Gray exhibited specimens of a new manner of en- 

 graving on stone, well adapted for botanical and other 

 natural history illustrations. The cost was stated to be very 

 low compared with copper-plate engravings. 



A paper containing an elaborate description and drawings 

 of the anatomy of the animal of Helix alholabris, Say, by 

 Joseph Leidy, M. D., of Philadelphia, Corresponding Mem- 

 ber, was read, and referred to the Publishing Committee. 



A letter from Dr. C. T. Jackson, dated at Copper Harbor, 

 Lake Superior, Aug. 12, 1845, was read. Dr. J. described 

 a large block of native copper discovered by Major Camp- 

 bell on the lake shore, about 40 miles west of Keweenan 

 Point. It measured 3 feet 4 inches in length, by 2 feet 5 

 inches in width, and 7 to 10 inches in thickness, and weighed 

 about 2000 lbs. Its surface is deeply cut by grooves of 

 abrasion, and is covered with fine drift scratches. It was 

 found among loose blocks of sienite on the beach, nearly 

 covered by gravel. Dr. J. considered it to be a valuable 

 geological specimen illustrative of drift phenomena. 



Dr. J. also related some particulars concerning the vein of 

 black oxide of copper near Fort Wilkins. The ore occurs in 

 bunches 5 or 6 feet long, and generally S inches thick in the 

 middle. The bunches run out into dead vein-stone of cal- 

 careous spar. The principal ore in the mine was stated to 

 be the black siliceous oxide, mixed with or covered by chry- 

 socolla or green hydrous silicate of the oxide of copper. 

 Laumonite and analcime abound also in the vein. Dr. Jack- 

 son supposed the chemical action producing the various 

 minerals to be as follows. They resulted from the action of 

 lime on gelatinous silicate of alumina. The oxide of copper 

 was precipitated from the gelatinous silicate by the action 

 of lime, and black silicate resulted from the influence of 

 heated water, while green silicate formed when the water 

 was cold : when lime predominated, the black oxide was 

 precipitated pure ; but when there was a deficiency of it, 

 the silex combined with the oxide of copper. Laumonite 



PROCEEDINGS B. S. N. H, 8 OCT. 1845. 



