a 
293 
of Mr. Mallet, which have so lately been before the Academy, 
show that even the elasticity of granite is lowered by its joints 
and veins almost to a parity with incoherent sand. A gradual 
change of direction, such as is given by the little valley that 
I have described as intervening between me and the Termi- 
nus, has no effect ;-but I think that a more considerable one 
might exert considerable power in deadening the wave. It, 
therefore, is not unlikely that a mass of discontinuous rock, 
rising abruptly one or two hundred feet above a railway, 
would be but little affected by it. 
