344 REPORT ON NATIONAL MUSEUM, 1886. 



form of seams which are parallel to the lines of bedding or distributed 

 in short, interrupted laminae. These seams, whether continuous or 

 otherwise, are fatal to the integrity of the stone, and there is scarcely 

 a limestone structure in the country, of twenty-live years standing, 

 which is not more or iess dilapidated or unsightly, from the effects of 

 absorption of water by the clay seams, and the alternate freezing and 

 thawing. When laid in the position of the original beds, which is the 

 usual mode, the separation by the clay seam is slower; but when used 

 as posts or pillars, with the lines of bedding vertical, the change goes 

 on more rapidly." 



Sandstones, on account of their widely varying textures and degrees 

 of compactness, together with an equal variation in composition and 

 character of cementing materials, are influenced, to a greater or less 

 extent, by all the atmospheric influences enumerated. In the order of 

 its apparent importance may be mentiond first the effects of freezing. 

 As will be noticed by reference to the tables in the appendix, sand- 

 stones will absorb from about one-fiftieth to one eighth of their weight 

 in water in twenty-four hours, or from _5 per cent, to 12J per cent. The 

 approximate amount which a stone may absorb with impunity cannot, 

 of course, be stated, since much depends on its position in a building 

 and the strength and structure of the stone itself. It is not too much 

 to say, however, that any stone which will absorb 10 per cent, of its 

 weight of water during twenty-four hours should be looked upon with 

 suspicion until, by actual experiment, it had shown itself capable of 

 withstanding without harm freezing when in this condition. Half of 

 this amount may be considered as too large when the stone contains 

 any appreciable amount of calcareous or clayey matter. (See foot-note, 

 p. 348.) 



It is to their great absorptive power that is due the large amount of 

 disintegration and exfoliation seen in the softer sandstones, as the Tri- 

 assic of the Eastern United States and the sub-Carboniferous of Ohio. 

 When a stratified rock, and especially one that is distinctly laminated, is 

 placed on edge the water filters into it from above, and, there freezing, 

 from necessity produces the scaling so often noted in the Connecticut 

 brownstone. If placed on the bed the effect is not nearly as disastrous, 

 but with a porous stone the effect of continual freezing and thawing can 

 but be injurious. It was with an apparent entire disregard of the prob- 

 blc effect of these agencies that was selected the soft and porous Juro- 

 Cretaceous sandstone from Acquia Creek, Virginia, for the construction 

 of the White House, central part of the Capitol, and other public and 

 private buildings in Washington, a stone so susceptible to these influ- 

 ences, that it is only by a most prodigal use of paint and putty that the 

 buildings are kept in a condition at all presentable.* 



* Other reasons than that of lack of durability can be given against the use of 

 a too porous stone in a house wall. "A red sandstone house may be a very handsome 

 building, but then it may bo holding tons of water, and sueh a wall, if exposed to the 

 northwest, in an open country, in our neighborhood, in a rainy winter, would, no 



