l8o NEW YORK STATE MUSEUM 



and 1842 of dolomitic marble from Ossining. The outer walls are 

 roughened by pitting and scaling, and the cornices, lintels and 

 columns are so much disintegrated by solution and frost as to 

 present a very bad appearance. The stone is coarse and mealy 

 in texture, ill suited for building purposes. 



The composition of a marble, so far as relates to the relative 

 percentages of calcium and magnesium, probably has a very sub- 

 ordinate influence upon weathering qualities. Much more im- 

 J3ortant is the texture, and this is a feature that varies greatly with 

 each particular quarry. The size of grain is not necessarily an 

 indication one way or the other ; though the coarse stones may 

 possess larger and more continuous pores, their grains present re- 

 latively smaller surfaces to the attack of solvents than do the fine- 

 grained sorts. The main elements determining the weathering qual- 

 ities are the degree of compactness and the coherence between the 

 grains. These can be ascertained by physical tests for porosity 

 and tensile strength, and by study of thin sections under the 

 microscope. 



The presence of silicates in large crystals is detrimental to marble 

 used for outside work, since there is not the same coherence between 

 the crystals of silicates and those of the carbonates as between the 

 carbonates alone, and consequently moisture gains access along their 

 boundaries. Sulphides are still more obnoxious, not only produc- 

 ing iron stains, but also causing decomposition and pitting of the 

 surface through the action of the sulphuric acid which is always 

 formed by their oxidation. 



Dale ^ has made some interesting observations on the effects of 

 the New England climate upon marble monuments and tombstones 

 and states that white marbles after exposure for 75 or 100 years 

 have so far weathered as to indicate the complete efifacement of 

 the lettering within 300 years of the date of cutting. 



Smock ^ gives as a quotation, the following notes in regard to 

 the durability of the Gouverneur marble : 



The Gouverneur marble was employed at least fifty years ago for 

 gravestones, and in the Riverside Cemetery, at Gouverneur, these 

 old gravestones, bearing the dates from 1812 onward, can now be 

 seen. As compared with the white marble headstones from Ver- 

 mont it is more durable ; and there is not so luxuriant a growth of 

 moss and lichen as on the latter stone, but in the case of the older 



1 The Commercial Marbles of Western Vermont. U. S. Geol. Survey Bui. 

 521, 1912, p. 38. 



2 Building Stone in New York. N. Y. State Museum Bui. 10, 1890, p. 237. 



