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THE POPULAR SCIENCE MONTHLY. 



ground. Again, huge nuggets of copper, torn from the immense de- 

 posits of native copper at Keweenaw Point, Portage Lake, and the 

 Ontonagon district, on the southern shore of Lake Superior, are found 

 widely disseminated to the south of these localities in Michigan,Wis- 

 consin, Ohio, and Minnesota, a few of which have weighed 300, 800, 

 and one 3,000 pounds. From the sides of the White Mountains frag- 

 ments of rock have been carried away, and not only conveyed south- 

 ward, but, as Agassiz first pointed out, distributed northward, though 

 only at comparatively slight distances. Long Island, that narrow 

 fork of land running eastward and separated from the southern shore 

 of Connecticut by the Long Island Sound, a shallow and turbulent 

 trough, is lined, alike on its southern and northern edges, with bowl- 

 ders, while its backbone of low hills is also strewed with their debris. 

 They occur gathered together in groups forming topographical feat- 

 ures in the landscape, and single ones have a weight of 2,000 tons. 

 As regards their origin, they seem to have drifted from three localities, 

 from the Helderberg Mountains in Central New York, from Manhat- 

 tan Island, and from various points in Rhode Island, Connecticut, and 

 Massachusetts. Those about the west end of the island may be 

 traced to the Eastern States lying to the north, while many of the 

 western visitors appear to have approached along the valley of the 

 Hudson from the Highlands of New York. On Staten Island we may 

 trace still farther the current of traveled rocks, and find both centres 

 of emigration represented: the bowlders, now gray with lichens, half 

 emerging from the soil, or deeply buried beneath gravel, clay, and 

 sand, or else dispersed in colonies over the surface like pebbles on a 

 board. Manhattan Island, along its southern shore, has been dotted 

 with bowlders of serpentine, dragged from Hoboken, while gneiss and 

 anthophyllite from the bed-rock of the island, limestone from Kings- 

 bridge, and jasper from the Palisades, have likewise been sown across 

 it, though before the restless advance of population they are fast dis- 

 appearing. In Westchester, Putnam, and Orange Counties, along the 

 banks of the Hudson, these bowlders, all indicating northern extrac- 

 tion, are repeatedly found, frequently at heights of 1,000 feet. These 

 erratics have come from the Shawangunk Mountains, from Whitehall, 

 Essex County, and from Potsdam ; in short, they are witnesses of an 

 invasion of northern material prevalent over the State. That these 

 rocks belong northward is not difficult to prove. The reasoning is 

 simply this : When anthophyllite, for instance, a rock unknown in 

 situ to Long Island, appears there in broken and detached masses, 

 we must conclude it belongs to the nearest deposits of the same rock, 

 where it occurs in place, as upon Manhattan Island, and the horn- 

 blendic rock, the gneiss, trap, and iron-ore, similarly found on Long 

 Island, we refer to those conspicuous and well-known localities in Con- 

 necticut and Rhode Island where exactly these rocks, identical in 

 chemical composition, are quarried. 



