QIJAKKY MA'I l',RIAI,S OI<- NICW YOKK 6l 



sloiic scrvicc.'iMc foi' iiolislicil :\\\i\ (|c(oi";il ivc work. 'I he (Iccp 

 j^jiX'i'ti of llic Adiroiid.'irls syciiilc is very rliaraclcrisi ic. Aiiorl liositc 

 is c'itluT ^y:iy or dark' ^rvv.u, the Killer hciiif^ chaructcrislit: of the 

 fcl(ks|)ar ill its ori^dnal state, while Loay is jjcculiar to the crushed 

 and recryslani/.cd varieties. The nnernshed feldspar sliows the 

 bhie iridescenee conimon lo lahiadorile whitli adds iiiik li lo ihe 

 beauty of poh'shcfl samples. 



'I'liere are no pernliarilies in the. weatherin}.( of tlu; two rocks, 

 and tiiey yield Ihe same decomposition ])r(jdiicts nanicfl under gran- 

 ite. On the whole, syenite appears more resistant to frcjst action 

 than the latter, at least it seldom breaks np into a j^raiiiilai' -A^ffra- 

 gate which not infrefpiently marks the oulcroj) of granite- bodies. 

 As to the durability of anfjrthosite, little can be said from tlu- point 

 of practical e.xjieriencc- since it has not been used very lon^ for 

 outdoor work. The rock, in ]jlace, shows bttlc change ow the 

 surface. At Augur lake, near Keeseville, there are vertical cliCfs 

 of anorthosile which have been direetjy exposed to the; weather 

 ever since the glacial period ; these show a bleached film not more 

 than one-fourth of an iixli thick coating tlu; surfaee, but no stain 

 or softening. This appears a favorable indication of its jjermanency 

 under atmos|>heric conrlitions. 



DIORITE 



The name diorite is used to denote a rock containing plagioclasc 

 and hornblende as essential miiieials. The plagifjclase is nearer the 

 albitc than the anorthite. end of tlu; series, including such varieties 

 as oligoclase and andesine ; the hornblende is the same !:iiifl that 

 accompanies syenite or granile and is usually ])leiilifnl. 'Ihe rolor, 

 consecjuently, is ralher dail;, with the grayish tones predoniinating. 

 Some diorites contain considerable bifjtite which, if it gains ascend- 

 ency over the hornblende, makes a mica-difjrite as flistingnisbcf! frf)m 

 the hornblende tyjic which is simply a diorite. The cfjinposil ion of 

 the fliorite is iiitermediate between that of granites on one side and 

 the gabbros on the (jther, and it might be expected to lind gradatifjn 

 toward either series, through the apju-arance of certain characteristic 

 minerals. The mingling of f|nart/. and alkali feldsjjar makes a 

 rather comnuju variation horn the ty]>e, leading to the class of 

 granodiorites which may be described equally well as basic granites. 



The fliorites are not common rocks in this State. There are no 

 large areas of ly])ical massive diorite; some of the gneisses in the 

 Adirondacks are related to diorites in mineral comjjosition, having 

 perhaps originaterl frrjm such rocks, though now changcfl to the 



