DOME STRUCTURE IN CONGLOMERATE 569 
Gilbert? suggests three processes, all of which, according to him, 
may be concerned in the formation of domes, viz.: (a) secular changes 
in temperature (he dismisses annual and diurnal changes because 
their influence penetrates but a small distance); (6) expansive force 
developed in weathering, and (c) dilation from unloading. 
A Ge-S 
re ‘ 
W-<=— > --1W" \ 
Fic. 8.—Graphic representation of some of the forces effective in dome formation. 
WW’=expansive force due to weathering, acting at A, B, and C. 
GG’=weight of overhanging or loosened block effective at A, B, and C. 
WW’—(GG”-+ cohesion and adhesion of conglomerate) =EF=effective force 
tending to formation of crack. 
The component of EF acting in the direction WW”, and G’’G’ tend to removal 
of loosened block; these two forces become less and less as the slope of the dome 
surface decreases, reaching the value zero at the point where the tangent to the surface 
is horizontal; where the tangent is vertical they have their maximum value of WW’ 
and GG’, respectively. The scaling process is, therefore, most effective on vertical 
faces, becoming less and less so as the faces approach the horizontal. 
CONCLUSIONS REGARDING THE ORIGIN OF CONGLOMERATE DOMES 
The conclusions reached by the writer, regarding the origin of the 
conglomerate domes just described, involve both of the two general 
theories previously given, and may be tentatively stated as follows: 
In the first place they are locally hardened portions (gigantic 
concretions, if you please) of a practically homogeneous conglome- 
t Loc. cit., p. 32. 
