Mr. Matter on the Dynamics of Earthquakes. 63 
where in London, for that the solid ground every where vibrated by the rolling 
of carriages, &c. 
Captain Denman, R.N., found by experiment that the vibration of the 
ground, produced by the passage of an ordinary goods train upon a railway, 
extended laterally more than eleven hundred feet from the line, in marshy 
ground, over sandstone. He also discovered (what is very interesting as respects 
our question) that the vibration only extended about one hundred feet vertically, 
when tried above a tunnel in sandstone rock. Houses and towers rock with the 
wind; Salisbury spire moves to and fro in a gale more than three inches from 
a plumb line. Tall chimney stalks of manufactories, when first built, will 
vibrate four or five inches, by a man merely rocking himself backwards and 
forwards upon the top, and various other instances might be cited. In all these 
cases, however great the aggregate motion of the whole vibrating body, there is 
no breach of continuity of its particles while ever they oscillate within its specific 
elastic limits. 
In the collieries of the thick seam coal in the north of England the fire clay 
and sandstone roof is supported by temporary props of timber during the cutting 
out of the pillars of coal, and finally these props are withdrawn when large areas 
have been wholly exhausted of coal. The roof is then suffered to drop down, 
and the whole supereminent mass, up to the surface, often consisting of a thou- 
sand feet in depth of strata of shale, sandstone, coal, &c., becomes fractured, breaks 
down, and subsides upon the floor of the former coal seam. The fracture and 
subsidation of these colossal masses is not only attended with the most awful 
noises underground and at the surface, but with shocks felt in the neighbourhood, 
which precisely resemble earthquake shocks, though less violent. A powerful 
blow produces quite similar effects upon the solid mass of the earth. At the 
latter end of last century, one or more of the great vertical and impost stones 
of Stonehenge suddenly fell down: the concussion produced a wave, which was 
transmitted around in every direction, like that upona pool of water into whicha 
pebble has been dropped, and the shock felt in all the neighbouring hamlets was 
so great that for some time, until the cause was discovered, it was thought to have 
been an earthquake, as in fact it was, though not produced by natural causes. So 
also when the great Spanish powder magazine, said to have contained 1500 barrels, 
was blown up, near Corunna, at the conclusion of Sir John Moore’s retreat, I 
