858 The Philosophy of Earthquakes. 



flat fork-moss ; F. viridulus, green flat fork-moss ; F. osmund- 

 oides, Alpine flat fork-moss; F. asplenoides, fern-like flat 

 fork-moss ; tliese all having terminal fructification ; and F. 

 tamarindifolius, short-leaved flat fork-moss, with an axillary 

 cladocarpous fructification. 



THE PHILOSOPHY OF EARTHQUAKES.* 



In our last number we collated the principal facts connected 

 with the British earthquake of October, 1863, and made a few 

 observations, preliminary to a more particular study of this 

 class of convulsions. Let us, in resuming the inquiry, first 

 endeavour to form some conception of the earth, or rather of 

 its crust, or outer portion, as a whole. We must not figure it as 

 a quiescent body, which would be far from the truth, but 

 regard it as undergoing incessant change, under the action of 

 forces operating in different directions, and producing con- 

 trasted effects. For two thousand years astronomers know 

 that our globe has made no change in its diameter sufficient 

 to produce any recognizable effect, and it may have been 

 equally still in this respect through time-periods of inconceiv- 

 able extent. Yet we cannot imagine that at any time its 

 various formations were absolutely at rest. On the surface, 

 rivers are constantly carrying down to the sea myriads of tons 

 of solid matter taken from adjacent lands ; atmospheric 

 influences disintegrate and crumble various rocks, and other 

 agencies constantly take to pieces the structure that exists. 

 On the other hand fresh strata and fresh structures are being 

 formed, with equal continuity of operation, and if one set of 

 forces tend to pull down and level, another set of forces pro- 

 duce upheavals and diversities of height. 



Sir Charles Lyell gives a beautiful illustration of this action 

 and counter action of forces, when he instances the case of a 

 large river bringing down sediment which gradually fills up a 

 sea hollow 2000 feet deep. If elevation then takes place to 

 the extent of 2000 feet, we shall have a mountain of that height ; 

 but if our sea bed had been raised before the 2000 feet of 

 river sediment had been deposited, instead of a mountain wo 

 should only have had a shoal. Thus, when earthquakes arc 



* The Fir* I Principles of Observational Seismology, as Developed in the Report 

 io tlie Royal Society of London of the Expedition made by command of (lie Society 

 into (lie interior of the Kingdom of Naples to investigate the circumstances of the 

 greal Earthquake of December, 1857, by Robert Mallet, O.E., F.R.S., F.GhS., 

 M.K.I.A., etc., etc. Two vols. Chapman $ Hall. 



British Association Earthquake Catalogue. Taylor fy Francis. 



