. Guide leaflet. miles ormore below the present sur-face of the earth, for in addi-tion to closely appressed folds,they show flowage structuresand oftentimes segregationof the quartz, feldspar, andmica ingredients into sepa-rate bands. Where the Manhattanschist is unweathered, itaffords good foundations forbuildings. Where it is weath- ered, it shows a l)rownish to rusty appcar-auvv caused l)y the oxidation of the ir(jnl)resent in the l)i()tite. Weathered surfacesappc^ar in the rock along joint planes andon surfaces which have been exposed for along time. Where the surfaces showglacial marking
. Guide leaflet. miles ormore below the present sur-face of the earth, for in addi-tion to closely appressed folds,they show flowage structuresand oftentimes segregationof the quartz, feldspar, andmica ingredients into sepa-rate bands. Where the Manhattanschist is unweathered, itaffords good foundations forbuildings. Where it is weath- ered, it shows a l)rownish to rusty appcar-auvv caused l)y the oxidation of the ir(jnl)resent in the l)i()tite. Weathered surfacesappc^ar in the rock along joint planes andon surfaces which have been exposed for along time. Where the surfaces showglacial markings, the weathering is slightand of no consequence. In long exposedsurfaces the weathering may have reacheddepths of two to four feet, and in somenarrow zones, even to forty feet. Infact, in some cases, the decay of the vari-ous mineral ingredients may have pro-gressed to such an extent that the rockmay be crumbled in the hand. On flatsurfaces the decayed rock will carry aload, but on exposed vertical walls it will. Reeds, N. HANGING MASS OF GRANITE PEGMATITEShowing bulkhead wall, slip No. 3, foot of West 51st Street,New York City. The rock is steeply inclined and jointed 172 NATURAL HISTORY
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectnatural, bookyear1901
