QUARRY MATERIALS OF NEW YORK 179 



strong durable stones; others are made up of rounded, smooth 

 particles which simply adhere without interlockment. The latter 

 kind are less durable. 



WEATHERING QUALITIES 



Marbles are much more subject to solvent action when exposed 

 to the weather than the silicate rocks, and the effects of solution 

 upon most marbles exceed those of mechanical agencies in pro- 

 moting decay. Pure water, however, has little solvent power upon 

 either calcite or dolomite; the action of atmospheric moisture de- 

 pends upon the small amounts of acid constituents which are ab- 

 sorbed from the air. All rain water contains carbonic acid, and in 

 cities where the consumption of soft coal is large it carries also 

 more or less sulphuric acid formed by the combustion of the sul- 

 phide impurities in the coal. It may be expected, therefore, that 

 the same marble will weather more rapidly in a humid climate than 

 in a dry one. Fog and mist have an accentuated effect as they 

 absorb relatively large proportions of the acids and enable the 

 moisture to penetrate deeply into the stone. 



A dolomite marble, under the same conditions and of equal 

 quality in regard to textural characters, should prove more resistent 

 to ordinary weathering agencies than a calcite marble. The fact is, 

 however, that many dolomites succumb rather rapidly on exposure 

 to the weather, as is shown in some examples that have been em- 

 ployed for building purposes in the East. Decay in these cases may 

 be attributed mainly to the possession of an open weakly bonded 

 texture which facilitates the penetration of moisture and attack by 

 frost. 



The dolomite marbles of southeastern New York include ex- 

 amples of exceptionally good building materials which have with- 

 stood well the severe tests of our climate and also others that have 

 decayed rather rapidly under the same conditions. Smock ^ has 

 given particulars of the relative durability of different marbles used 

 in New York City, and states that some of the dolomites have a 

 durability compared with that of the best sandstones. The old 

 United States assay office in Wall street was built in 1823 of Tucka- 

 hoe marble ; though yellow from age, the surface remained smooth 

 and the edges sharp, whereas the Italian marbles used in the caps 

 of the columns were much weathered. An example of rapid decay 

 is found in the State Hall in Albany which was built between 1835 



1 Building Stone in New York. N. Y. State Museum Bui. 10, 1890, p. 292-94. 

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