Mr. Matter on the Dynamics of Earthquakes. 93 
the same substance, or, in general, of any force whatever transmitted by 
pulses. 
Here, again, we want numerical data. Hassenfratz and Gay Lussac 
observed, in the quarries under Paris, that sound travels with immense velocity 
in rock, and the same observation has been made in blasting the rocks in the 
Cornish mines; but no measwres of its velocity have been ascertained, and the 
only trustworthy measurements we possess, of the velocity of sound in any 
mineral solids, are those obtained by Biot, as to the time of wave transit through 
cast iron. He found, as has been previously stated, that sound is transmitted 
through cast iron at the rate of 11,090 feet per second. 
If we take the modulus of elasticity for the following rocks from the pre- 
ceding table, and, comparing these with the modulus of cast iron, suppose the 
time of wave transit in each to be proportionate roughly to the square roots of 
their respective moduli, we get the following table of results for the specific 
period of the great earth wave, or shock, through the several sorts of rock 
formation. 
Period of wave transit, or 
velocity in feet per second. 
Tuimestone (softiLias); 6-1) =) lehesh « pallbalm -) os, (ree) «93040 
Sandstone (millstone grit), . . . . - + + « « « + « 5248 
Portland stone\(colite); ©.) (3 3 30 8 4 a sw ONL 
Limestone (primary marble), . . .....- =. + - 6696 
Limestone (hard carboniferous), . . - .- .. - +. + 7075 
Clay slate (Leicestershire), . . . . - » - - + + + « 12757 
Comparing these numbers with the observed speed of the great Lisbon earth 
wave or shock, namely, 1750 feet per second, we find that the result agrees 
sufficiently, making allowance for the loose superficial deposits in which the period 
of the Lisbon wave was observed, and for the retardations produced by breaches 
of continuity therein. Let it be understood, however, that no present importance 
attaches to any of these numbers, which are all but crude approximations, and 
to be viewed as mere illustrations of the application of my theory, rather than as 
proofs of, or deductions from it. 
When correct data shal! have been obtained, when we have found the mo- 
duli of elasticity, and of cohesion, and the limits of extensibility, for all our 
great rock formations, and the changes produced in these by augmentations of 
temperature,—a work capable of easy performance, but requiring multiplied 
