74 
REPOBT—1847. 
of deposition must generaUy have been so exceedingly slow when considered 
with reference to extensive areas, as to leave little or no doubt, I think, 
that the positions of the isothermal surfaces at any proposed time during 
the process of deposition would approximate extremely near to that limit 
beyond which they could not have passed had the deposition ceased at that 
time. In such case, the ascent of the isothermal surfaces and the couse- 
quent columnar expansion would necessarily cease soon after tlie deposition 
of the whole sedimentAry mass was completed, and could never be effective 
in raising the surface of the mass above the level of the sea. 'fhe theory 
would therefore fail to account for the elevation of tho surfaces of whole 
continents to coni^iderable heights aliove that level, the only great phaiio* 
menon of elevation, perhaps, which we could profess to account for by 
columnar expansion. 
Section II. Vibratory ^fotions ofthr. Earths Crustprodwedhy Suiter- 
ranean Forces — Earthi/uaheit. 
33. In the preceding articles I have considered the mechanical effect* of 
subterranean forces in elevating and dislocating the portions of the solid 
crust of the earth iitmiediately superincumbent on the fluid matter, in which 
forces have been snpposed to originate. Other mechanical 
eifects would also result from these sudden dislocations and the explosive 
^'^*ch would doubtless accompany them. l“be effects I allude to are 
the vibratory motiorw which would be excited in the solid or fluid masses 
in the immediate vicinity of tlio disiurbed district, and propagated with great 
rapidity to others more remote. In those great, disrnplions which we have 
heretofore contemplated, those vibrations would be of great intensity near 
the repons where they originated, ami it is possible that they uiight extend, 
flhn ''^'2' l>ortions of the globe, before tlieir intensity 
should become sufficiently weakened to be no longer seuslblo. These 
econ ary e eets of the great olevatiug forces wJiich have left so many pli®’ 
anv ctfccte, not bcifig calculated to produce 
Shfrff- niodihcation of character in the rocks through which the 
are matters of little interest to geologists as «• 
ff become, or. tk coutninr. 
Manr.^linn^T ’ with reference to modem earUiquakes. 
vibrations lit* ♦! those phroaoinena as duo in a great measure to 
underTur merit,oned *, and U.e sulycct has lately been brought 
QuakL’t in whth'V® ‘ ‘be Dynamics of Earth- 
in more’detail rhn troat^ it in a more determinate manoer. anil 
Se manner in «) - h V Writer. I n„w proceed to consider 
tfie maunor in which vibratory motions may be generated and oronagated 
inn- UiP mnr * ^ **wbp‘Ct more easily understood if I begin byexphun* 
mg tlie more simple emma of the propagation of such motions® ^ 
oflbe Propagation of vibratory Jfoticn. 
«pacJ subject become much simplified when the 
t^ds, 1; 3 the Vibnuion* ex- 
^ ^ * that into winch they are subsequently propa* 
reason^o'TnSpLuSnJJtrJ^m^^ rarthquakc extcmls further than there is wf 
earth newly in the eainc^nuer os a^mirrl Probably proptsated through the 
turea ou Natural Philosophy, vol. i » 717 through the air.’’-youDg’» ^ 
t Procrodiuga of the Koyal Irhli i'eademy, vol xxi. part 1. 
