(hi ('ijcJix iif S<'iJ',iti<nf<tti(iii. — W'iJlittnix. '-'i'lX 
the already existing elevation. Tlii« recipnx'ity of etl'ects would. 
however, he antagc^iized by at least three counter- tendencies: 
1st. the earths tendency toward sphericity due to the combined 
action of gravity and its rotational movement. 2d, the rapid re- 
adjustment by erosion which would ensue from such enormous 
differences of level. 3d, the disturbed etiuilibrium of the inter- 
nal ftuid which normally will assume concentric shells with den- 
sities inversely proportional to the distance from the centre. All 
these would oppose the distorting forces here contemplated ( and 
all others producing like effects), and confine the surface move- 
ments within rigid limits. Here it should be borne in mind that 
when the upheaval and consequent expenditure of mechanical 
energy is great, the energy assuming the form of lu-at (due to 
crustal friction) is proportionately diminish(^d. so that tlu' result- 
ing evaporation of oceanic waters, and, hence, the violence of 
watery precipitations is diminished, but. so fai' as erosion is con- 
cerned this loss is offset by the increased angle of elevation of 
continents. \ am convinced that the heat generated by crustal 
friction is an important factor in the processes of erosion: for. 
when developed in emergent land, it will increase the chemical 
effectiveness of atmospheric moistuiv coming in contact with it. 
and thus accelerate disintegration. Where, on the other hand, 
it is developed in the oceans Ited it will heat the cold polar cur- 
rents there, part of it Itcing tlius conA'eyed to the e(juatorial 
regions there to augment evaporation, and part of it will pass 
directly by convection to the surface producing a like effect. In 
the reciprocal elevations and subsidences heretofore alluded to 
the heat of friction (and consequent evaporation resulting in 
erosion), would be developed on a prodigious scale. Tiiis would 
promote the lapid leveling mentioned above. 
Thus it ai)[)ears that by an api)eal to physical priiu-ipk's 
we can exi)lain the fact of perio<licity in the cycles of sedi- 
mentation ;is ;i I'esiilt of several independent forces. While 
we cannot hope in any given instance to refer a partic- 
ular u|)heaval or subsidence to a six'citie eategoiv i)f causes, 
yet we may rest assured that one or several of these causes 
have been operative either isolatedly or conjointly in produc- 
ing the varied effects. Doubtless minor local disturbances 
are referable in soiih' cases to purely loc;il causes, although 
Ave should not trust too implicitly to such an interpretation. l>e 
