\Ik HOPKINS, ON UFSEARCHES IN PHYSICAL GF.OLOOY. 11 



inn.ss throujjli tlio moiliuui of some tliiiil. wliii'li mav lu- i'oiuvi\i>il to 

 be lUi oliistic vapour, or in othcv lasos a mass of luattor in a statc 

 of fusion from hoat. Kvory ovologist. I i'onivi\t\ wlio admits tlir 

 action of i-lovatory foroos at all. will hv ilisposcil to admit tlu> li>i>iti- 

 macy of tlioso nssuniptions. 



Tlu- tirst otli'i't of our <.li'\atoiy t'ori'o. will ot' I'oursi- ho to raise 

 tlic mass under whieli it aets. and to plaee it in a state of r.rfi'iixioit. 

 and eonsiHinently of Iriisioti. The inerease of infensitN in the elexatory 

 foree mioht he so rapitl as to "ive it the eiiaraeter of an impulsive 

 foree. in whieh ease it woulil he impossihle to ealeulate tiie ilisloeatini; 

 erteets of it. This intensity and that of tiie eonseijuent tensions will 

 therefore he always assmned to inereasi> coiitiinioitshi, till the tension 

 l)eeomes sutlieient to nijiture the mass, thus proilueino' fissures and ilis- 

 locations. the nature ami jiosition of >vhieh it will lu- the first objeet 

 of our investigation to determine. These will tlepend partly on the 

 elcvatory foree. and partly on the resistanee ojiposeil to its aetion hv 

 the cohesive power of the mass. Our hypotheses respeeting the con- 

 stitution of the eli\ated mass, are by no means restricted to that of perfect 

 homogeneity; on the contrary, it will be seen that its cohesive power 

 may vary in general, acconling to any continuous law ; ami moreover, 

 that this junver, in descending along any vertical line, may varv accor<ling 

 to any diswntinuous law, so that the truth of owx general results will he 

 independent, for example, of any want of cohesion between contiguous 

 horizontal beds of a stratified portioi\ of the mass. Vertical or nearlx 

 vertical planes, however, along which the cohesion is umch less than 

 in the mass inunediatcly on cither side of them, may pnuluce con- 

 siderable modifications in the jthenomena resulting from the action of 

 an elcvatory ftMce. The existence of joints for instance, or planes of 

 cleavage in the elevated mass. su])posing the regularly jointed or slaty 

 structure to prevail in it previously to its elevation, might allecl in a 

 most im]U)rtant degree, the character of these pheitomcna. To a ma.ss 

 tlius c«>nstituled, thcsi> inxestigations nmsl not be coi\sidi'rcil as '>-en»'- 

 rally applicable. W^'tical or highly inclined plaiux of' less irsixtaiuc. 

 will only be assume<l to exist partially and irregvdarly in the elevated 

 mass. 



BS 



