ON THE DURABILITY OF BUILDING STONE 38 1 



whole block, and the complete destruction is a question of 

 time, so that the life of our brownstone front scarcely ex- 

 ceeds that of Its well-preserved owner. Near the earth this 

 scaling proceeds more rapidly, as can be seen in all struc- 

 tures where stone is so placed. The exposure to extremes 

 of temperature and an excess of moisture, both in the melt- 

 ing snows, which are often piled against these lower courses, 

 and that arising from the ground, when not stopped by a 

 damp course, appears to be the cause for this more rapid 

 decay. Another cause of decay is in the faulty construction 

 of walls, wherein no provision is made, by undercut mould- 

 ings to carry off the drip of the water, and by inclined sur- 

 faces. In the case of lintels and sills, so that it cannot sat- 

 urate the stone. The proper position, even when the sills, 

 lintels and water-tables are laid on their* bed, does not pro- 

 tect thoroughly. If there are horizontal surfaces where the 

 water cannot drain off freely and quickly. Polished surfaces 

 add to the strength In position, by conducing to a more 

 rapid drainage of the rain waters, than do the natural sur- 

 faces of quarry-face stone or the uneven ones of rough- 

 dressed blocks. They have no little hollows into which the 

 waters can collect, and so act upon the stone up to the point 

 of a saturated solution. The ancient Greek structures, of pol- 

 ished Pentellc marble, and the palaces of the Lombards, in 

 northern Italy, are evidence of the durability of smoothed 

 and polished surfaces. The old Gothic builders also appreci- 

 ated the Importance of smooth surfaces, as well as a proper 

 position in the wall. The glaciated ledges of our rock out- 

 crops, which shed the water rapidly, show the value of such 

 a surface for endurance."^ 



* " A smooth and sound rock surface, produced by glacial rubbing and polish, is 

 better adapted to endure the ravages of time than any artificially hammered surface." 

 — Dr. Robert Bell, Bull. Geol. Soc. of America, Vol. i, p. 306. 



