.4y 



On lE,artliqiia7ces, ■ lO-j 



"its surfaco, but not siifTicient to cover the whole. The rocky floor is 

 wncovered, and peeps out in thousands of places. The dwellings we have 

 erected are built, some of them upon the beds of loose earth and others upon 

 the rock. Any shock given to the earth's crust as great in proportion as a 

 blow of a hammer to an ordinary sized table, would produce vibrations 

 sufficient to overturn or partially wreck houses consisting merely of small 

 stones piled one above the other, and if we return to our example of the 

 table we shall see that a Assuring of the rock would have the same effect. — 

 Many varieties of stone will crack upon the unequal application of heat ; 

 and were the leaf of a table composed of a single slab of stone, and were heat 

 or any other force to be so applied as to cause it to be suddenly fissured, tlie 

 resulting vibrations would be quite sufficient to set aii small objects upon it 

 in motion, causing some to fly in one direction and others in a different, while 

 still others would be whirled round, according to circumstances. What 

 would be the effect of one of those subterranean fissures running instanta- 

 neously for hundreds of miles through the solid rocky crust of the earth ? 

 We think that vibrations more or less violent would result. The effects 

 produced by nature with the same forces and materials are similar, no matter 

 whether the experiment be upon a small or large scale — upon a slab of stone 

 a yard square, or an area in the crust of the earth of the size of a continent. 

 When the tension exerted upon a mass of rock several miles in thickness is 

 sufficient to rend it asunder ; it would be indeed strange, were no vibrations 

 to result. The fissuring of the rock at a great depth, even although those 

 fissures might not extend up to the surface, would most probably be felt as 

 a more or less violent jar by the inhabitants of those countries immediately 

 above, while the sound might also appear like subterranean thunder, and be 

 propagated at very considerable distances. 



In all geologic ages those rendings of the earth^s surface have been of 

 frequent occurrence, and thousands of ancient cracks can be seen in every 

 rocky region, to occasion any one of which would require a con^^llsion equal 

 to a modern earthquake. Some of those fissures may be traced for a great 

 many miles, and, although in general, the rock on each side still remains in 

 its original position, and the parts in contact, yet in a large proportion of 

 the instances, the fissure is several feet or yards in width, and filled up with 

 new material, often veins of metallic ores. In many cases the country on 

 one side has sunk down to a greater or less depth, while the other remains at 

 its original level, thus producing W'hat the miners call a '' Fault," a word 

 which has been adopted as a technical term in geology. There is no forma- 

 tion which is not traversed by these fractures, and they may be seen in all 

 countries, thus proving that the whole surface of the earth has been subjected 

 in all ages to convulsions caused by the action of forces pent up in its 

 interior. 



We have no reason to believe that the causes which have operated so 



powerfully in ancient times to fissure the earth's crust, have ceased to exist. 



We are as yet in total ignorance of their nature, and for aught we know all 



those old catastrophes may yet be she',vn to have been occasioned by the 



13 



