348 REPORT ON NATIONA 



of rotten rock that bad accumulated during previous geologic ages 

 has been entirely removed, if the surface of the rock as displayed 

 in the quarry or natural outcrops preseuts a fresh and undecom- 

 posed appearance, this may be construed as a strong argument in its 

 favor, though it can not in all cases be accepted as conclusive.* A 

 purely calcareous rock may weather rapidly and yet leave no debris, 

 since its constituents are soluble and may all be carried away by 

 running water, leaving no traces to tell of the havoc going steadily on. 

 Impure limestones and all silicious rocks, however, leave more or less 

 debris as mark of their decay. 



But in regions south of the glaciated area the rock is still covered by 

 the decomposed mass, and hence no clew can thus be obtained. In 

 such cases one can only have recourse to structures that have already 

 been erected from the stone in question and there observe its weather- 

 ing qualities, or, if these are lacking, observe the stone in those parts 

 of the quarry that have not recently been worked. In opening a new 

 quarry, blocks should always be tested by allowing them to lie and sea- 

 son for at least a year before using. At the end of this time the pres- 

 ence ot any readily oxidizable pyrite will have made its presence known, 

 and the amount of disintegration, or induration, as the case may be, 

 will furnish a slight clew regarding its future behavior. Indeed, this 

 seasoning ot stone prior to its introduction into a building should always 

 be insisted upon, whatever its character. A good building stone, 

 whatever its kind, should possess a moderately fine and even texture, 

 with the grains well compacted, should give out a clear ringing sound 

 when struck with a hammer f and show always a clean fresh fracture. 

 It should also be capable of absorbing only a proportionally small 

 amount of water. $ 



across New Jersey; thence northwesterly across Pennsylvania into New York State 

 south, of Buffalo; thence southwesterly to near central Ohio; thence due south 

 nearly to the Ohio River; westerly along the river to a point north of Louisville, 

 Ky. ; thence northerly again nearly to Indianapolis, Ind. ; thence southwesterly so as 

 to include nearly all of Illinois; thence northwesterly to a point near Saint Louis; 

 westerly toward Jefferson City, Mo.; thence along the Osage River and northwest- 

 erly through Kansas near Topeka; through the eastern half of Nebraska, through 

 Dakota west of Bismark, and thence onward into Montana. 



* "No artificial structure or position will ever subject the stone to the same degree 

 of weathering influence to which it is exposed in its natural position. * * * The 

 rock which has withstood these influences is quite equal to withstand the exposure of 

 a few centuries in an artificial structure. " (Hall Rep. on Building Stone, p. '24. ) 



t In a report on some experiments on the transverse strength and elasticity of build- 

 ing stone, Mr. T. H. Johnson states " the resonance of each piece tested was propor- 

 tional to the modulus of elasticity as found by the test." (Rep. State Geol. of Ind., 

 1881, p. 38.) 



\ En un mot, les qualit6s essentielles des pierres tantdures quetendres sont d'avoir 

 le grain fin ot homogene, la texture uniforme et couipacte ; de resister a l'humidito 

 a la gelre, et de ne pas clater an feu en cas d'incendie. (Chateau, Vol. I, p. 272.) 



Any sandstone weighing less than 130 pounds per cubic foot, absorbing more than 

 5 per cent, of ir,s weight of water in twenty-lour hours, and effervescing anything but 

 feebly with acids, is liable to prove a second-class stone as regards durability where 

 thero is frost or much acid in the air." (Notes on Building Construction, p. 36.) 



