Mr. Mater on the Dynamics of Earthquakes. 91 
Two points remain, therefore, to be briefly considered, viz., what will be the 
velocity of transit of an elastic wave, so produced, in the various sorts of rock 
with which we are acquainted in the crust of the earth, and what will be the pos- 
sible elevation of the crest, and what the amplitude or length of the wave so 
produced. 
If our knowledge of the moduli of elasticity and of cohesion, of the various 
beds of softer or harder minerals, constituting the whole depth of loose or rocky 
crust of our globe, were perfect, we should be in a condition to answer these 
questions more perfectly ; unfortunately, however, no moduli of elasticity have 
been ascertained for mineral substances, with the exception of a very few, deter- 
mined for the use of the engineer or architect; these few I have tabulated 
below. Scanty as they are, they suffice to illustrate the truth of our theory, and 
to shew that, at this point, mathematics and physics can hereafter render the most 
direct and important services to geology. 
Modulus Extensibility 
of Elasticity. | before Fracture. | 
I MCE Ro: SSA AS to) 6 a. a ck ice oe Ome chain Mots 5.895.000 Ti0m 
WenwWirouphtnrons is wee hee ee Pre teers) ceed) PR ate ae ee 7.550.000 TIT 
ARR cashes tuil-nel> api olen serie ciusereiee: 0 eae [80-000 | 
Peeing er ca coe Mable. che siete shee 4.440.000 | 
| Limestone (maximum), « SI BLN ee ee. Be 2.400.000 
| —— (minimum), . Mealy ONS Cae S 635.000 | 
| Yorkshire sandstone (millstone exit), Se sti esate nies) cw 1.320.000 | 
| Slate, (Leicestershire), . . > HOtea sagas 7.800.000 
| White ITED LON Mien sVaRS) A cy Wr oitals, 4c Sullsrspbie. sinc 2.150.000 T3907 
IPOLHMANCESLONE EES ENE ie te Peres Mice te wet sete am cs 1.570.000 T7355 
le, LiCAGsre SMd | Subs at cisted cteriabsueed: pst co Pe<heve) lism, ap he ye ts stout sik eo 
| 
Referring to this table, we find, to take an example, that a mass of primary 
limestone will extend, before fracture, ;s,z part of its length; or, in round 
numbers, that every 1400 feet in length of a plain of such limestone may, by 
being bent into a curve upwards by any adequate force, be stretched one foot 
in length before rupture takes place any where; hence, if an area of only five 
miles in diameter, consisting of primary limestone, be elevated by any force what- 
ever, acting from beneath, its surface will be extended or stretched no less than 
eighteen feet, or rather more, before fracture takes place, and this, whatever be 
n 2 
