508s RALPH ARNOLD 
Those who support the theory of reaction from the surface differ 
as to the agent or agents which have brought about the result. 
Becker" believes the great granitic domes to be simply cases of exfoli- 
ation on a large scale, their regular curvature being due to the fact 
that, measured per unit volume, the surface exposed is in inverse 
ratio to the radius of curvature, so that the sharply curved surface 
weathers fastest. Furthermore 
he says:? “Weathering and 
abrasion proceed with a 
rapidity which increases with 
the surface exposed per unit 
volume. Hence these proces- 
ses lead to minimum surfaces. 
Therefore, also, the mathe- 
matics of erosion is essentially 
identical with that of capil- 
larity.” 
Fic. 7.—Section of dome at west end 
of Eagle Rock Valley, showing weathered 
3 : 
zone below overhanging block. Branner, from observations 
in Brazil, expresses the opinion 
that the even annual and diurnal changes and the approximately even 
penetrations of these changes cause the rocks to exfoliate or to shell 
off in layers of even thickness like the coat of an onion. Merrill4 
attributes exfoliation largely to temperature changes, but considers 
the curved partings in the rock below the exfoliating surface as the 
result of torsional strains. Chamberlin and Salisbury’ account for 
exfoliation on both a small and a large scale (including the dome 
structures of the Sierra Nevada) by great daily, rather than by great 
annual, changes in temperature causing expansion and contraction 
in the outer layers of the rock. They also consider the wedge work 
of ice effective in augmenting the scaling caused by expansion. This 
latter cause would necessarily be inoperative in that part of southern 
California in which Eagle Rock is located, for the temperature here 
seldom descends to 32° F. 
t Tenth Ann. Rept. U. S. Geol. Surv., 1890, p. 142. 
2 “Present Problems of Geophysics,” Science, n. ser., Vol. XX, 1904, pp. 551; 552: 
3 Loc. cit., p. 281. 
4 Loc. cit., pp. 180-84. 5 Loc. cit., pp. 42-44. 
