358 



ARCHITECTURE. 



Without multiplying instances, we may refer to the 



aqueduct at Rochester, which is already in a state 

 of dilapidation from exposure to the elements ; and 

 we could name a splendid public building, erected 

 from the crumbling marble of Singsing, which 

 promises an equally short-lived existence. It is a 

 dictate of common sense, that a knowledge of the 

 general structure of rocks, and the situations whence 

 the best materials may be obtained, is essential to 

 the builder and such as are charged with the erec- 

 tion of public works. A few hints on this subject 

 are all we have space to offer. 



A stone which is sufficiently durable underwater 

 may not be so when kept alternately wet and dry by 

 the rise and fall of water in a river, or canal, or on 

 a tidal coast, or even when wholly exposed to the 

 atmosphere. If it be a porous sandstone, it will 

 probably last well if constantly under water ; but, 

 if exposed to the air, the same rock will be certain 

 to crumble in climates subject to frost. Owing to 

 inattention to this simple fact, many of the finest 

 national structures of England, where there abounds 

 an almost inexhaustible variety of rocks of the most 

 imperishable quality, have gone to premature decay. 

 tl It is painful," says Philips, " to mark the injuries 

 effected by a few centuries on the richly sculptured 

 arches of the Normans, the graceful mouldings of 

 the early English architects, and the rich foliage of 

 the decorated and later Gothic styles. The chan- 

 ging temperature and moisture of the air, communi- 

 cated to the slowly conducting stone, especially on 

 the western and southern fronts of buildings, bursts 

 the parts near the surface into powder, or, by intro- 

 ducing a new arrangement of the particles, separ- 

 ates the external from the internal parts, and causes 

 the exfoliation or desquamation of whole sheets of 

 stone parallel to the ornamental work of the mason 

 From these attacks no shelter can wholly protect 

 the parts of a building which are below a ledge of 



