ELIZABETHTOWN AND PORT HENRY QUADRANGLES 23 



interesting material for the mineralogist. This limestone is a fairly 

 pure calcite. 



Overlying the limestone stratum at Port Henry there is another 

 of ophicalcite^ or of limestone speckled with included masses of 

 serpentine. This stone has been the object of quarrying and, fur- 

 nishing as it does, a variety having a white base with light and dark 

 green mottlings distributed through it, has commanded some 

 attention as an ornamental stone under the name of verde antique, 

 or Moriah marble. The serpentine is believed to be due to the 

 hydration and alteration of original diopside, whose unchanged 

 cores may be sometimes detected within the mass of serpentine.^ 

 This is practically the same rock as that which furnished the 

 E o z o o n c a n a d e n s e , to the early observers, but no good 

 specimens of this exploded organism have been discovered. 



A very characteristic minor associate of the HmestO'nes is a 

 lemon-yellow quartzite or quartz-schist, with more or less dissem- 

 inated graphite. The yellow color is doubtless due to decomposing 

 pyrites and the rock will ofte-n yield the astringent taste of iron 

 sulphate. 



Black and coarsely crystalline hornblende schist is also a common 

 associate of the limestone but in relatively small amounts. It may 

 contain large red garnets. The observer is often puzzled whether 

 to interpret this rock as an altered intrusive. mass of gabbro or as 

 a metamorphosed sediment. There are probably cases of both. 

 The remarkably regular masses which cut across the exposures, 

 and have a uniform and moderate thickness suggest an intrusive 

 origin most strongly of all. Over the Pease quarry just north of 

 Port Henry there is such a black band, and one courses through 

 another quarry in Pilfershire, southeast of Mineville. Along the 

 Delaware and Hudson railway tracks on the lake shore north of 

 Port Henry where there is an irruptive contact of gabbro and 

 basic syenite and limestone one can see the igneous rock tongu- 

 ing out into the Hmestone and apparently pinched off at times 

 by the dynamic disturbances. While it is entirely possible that the 

 hornblendic rocks have been derived from aluminous bands in the 

 original sediment, which might yield greater or less amounts of 

 hornblende, yet we are dealing with a district in which are numer- 

 ous intrusions of gabbro and basic syenite and where apophyses are 

 abundant. The marked plasticity of the limestone under pressure 



1 Merrill, G. P. Notes on the Serpentinous Rocks from Essex Co., 

 N. Y. etc. U. S. Nat. Mus. P^oc. 1890. 12:595-600. 



