et vie SOURCE JOrRy EVOLULION OF PRO= 
VINCIAL FAUNAS: 
Tue deformations of the outer portion of the solid part of 
the earth familiarly known as the ‘‘crust”’ are the result of an 
intricate combination of adventitious and systematic movements. 
The latter spring from the predominant action of the great 
stresses that affect the body of the earth; the former, from 
intercurrent variations in the expression of these dominant agen- 
cies due primarily to the rigidity of the earth, and secondarily 
to inequalities in its density, to changes in its internal tempera- 
ture, and perhaps to other conditions. Were the earth a homo- 
geneous liquid, the adventitious features would disappear and 
all its changes of form would be systematic, or if not absolutely 
all, at least all which seriously affect its deformation. While 
the adventitious movements that make for heterogeneity of con- 
figuration must be recognized, it is the function of the geologist 
to discriminate and emphasize the systematic factors and to rel- 
egate the adventitious elements to their proper subordination. 
It is assumed that the fundamental movements which affect 
the earth’s form are centripetal and that the dominant fact in 
the bodily history of the earth is the shrinkage of its outer parts, 
as has been so signally urged by Suess. Its upward movements 
may be regarded as adventitious, since they are incidents due to 
the restraint which rigidity puts upon a perfect adjustment to 
the demands of its contractile forces, or to variations from sym- 
metry of substance or of temperature which only become effec= 
tive through its rigidity. In a slightly different and broader 
sense, the continents may be said to be adventitious while the 
ocean basins may be said to be normal. We must hasten, how- 
ever, to qualify this idea, for the ocean basins have obviously 
sunk beyond the normal level which the surface of the earth 
would assume, did not rigidity deform it. The uniform spher- 
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