LAE PROPE ME SOL CLEDING SLONES, FETC: I8I 
occurring thus is the lichen, which often covers the surface of 
the rock after the manner of a mat, thereby exerting a protective 
as well as a destructive influence. The covering which they form 
serves as a protection against the atmosphere, while the acids inci- 
dent upon their decay and the mechanical effects of their rootlets 
penetrating between the grains are a slow cause of disintegra- 
tion. Algz are also common, and often occur on the damp 
parts of a wall, causing discoloration through their own decay 
and the lodgment of fine dust particles. The effect of allowing 
creeping vines, such as ivy, to cover the walls of buildings is 
picturesque, but the practice is certainly injurious to the life of 
the stone. 
Careless methods of working and handliing.—The natural forces 
of destruction have been greatly accelerated, either through the 
ignorance of quarrymen and their total disregard for proper time 
and methods of quarrying, or through the carelessness of workmen 
in cutting, carving, and laying the stone used in building con- 
struction. There are probably thousands of buildings, con- 
structed out of stones, the lives of which have been shortened at 
least one half by improper methods of quarrying and handling. 
Quarrymen have been found moving stone with heavy charges 
of powder, or even dynamite, expecting to obtain dimension 
stone for building purposes. The heavy charges of powder not 
only destroy a large amount of stone, but they also shatter the 
cement and produce incipient joints in the blocks which may 
accidentally remain in dimensions sufficiently large for building 
purposes. The destruction of the cement and the production of 
incipient joints not only weaken the rock, but also facilitate the 
entrance of water, with the attendant dangers from freezing, with 
which we are already familiar. This method of quarrying not 
only materially lessens the value of the salable stone, but hun- 
dreds of tons of otherwise marketable stone is absolutely 
destroyed. The use of heavy hammers and sledges in split- 
ting the stone, by striking continuously along one line, short- 
ens the life of the stone in the same manner as_ heavy 
blasting. 
