612

GREENSTONE.

it may occur in globular concretions.—It is frequently in veins, amiis sometimes distinctly stratified.—In some instances this rock con-tains shells, or other organic remains.

CLocalities.) Greenstone is by no means an uncommon rockin the United States . Fine examples of columnar Greenstone occurin several parts of the range of secondary mountains, which extendfrom Newhaven in Connecticut to Northampton in Massachusetts .At Mount Holyoke, near Northampton , the columns, which are near-ly perpendicular, sometimes vary in height from 60 to more than 100feet; and are frequently articulated, like those of basalt. Theseprisms are very often hexagonal; and their diameter sometimes ex-tends to four feet.*—Other examples of columnar Greenstone, ap--parently forming the summits of several mountains, sometimes from200 to 300 ft. high, have been observed by J. Merrick, esq. inMaine , about 100 miles above Hallowell , on the Kennebec. Theprisms present from 3 to 6 sides; their edges are straight and welldefined ; and their general aspect is that of bricks standing on theirends.—A secondary Greenstone is found also at Belfast , Jackson,Brownville, and other towns west of the Penobscot river. ThisGreenstone, which has hitherto been observed in detached, insulatedmasses, abounds with shells and impressions of shells. Some speci-mens much resemble gray-wacke slate. The same rock occurs near-ly on the height of land between the Kennebec and Penobscot.—At llarpswell, in Cumberland Co. is found an uncommon variety ofGreenstone, through which numerous balls or spheroidal masses, ap-parently of garnet , are disseminated. These balls, of which nearlya hundred sometimes occur in a cubic foot, are easily separable fromthe mass, and are usually somewhat larger than bullets. This rockhas not yet been observed in situ.

(Uses.) When this rock breaks into prismatic fragments, itforms a very useful building stone.—Most varieties of Greenstone,when heated red hot, plunged into cold water, and pulverized, be-come a good substitute for puzzolana in preparing water-proof mor-tar for- the construction of wells, cellars, docks, piers, Ac.

Var. 2. GUEENSToxE-sLATE.t Jameson. The structure andfracture of this variety are slaty. The hornblende and feldspar, whichis compact, are nearl)' in equal proportions. It also contains a littlequartz or mica.

Greenstone-slate is usually a primitive rock. Sometimes it forms

* See Bruce’s Min. Jour. v. i, p. 139. Also North American Review, v. i,No. 3, p. 33 7 .

f Grunstein schicfer. Webseh.