450 WO (VEC ANIMES EIRILTON. 
been in constant progress somewhere since the inauguration of 
the pre-Cambrian lands and seas, and that life has been likewise 
continuous and self-derivative, may be accepted as fundamental 
postulates. If, therefore, we seek for absolute divisions we 
doubtless seek in vain. But this does not dismiss the question 
whether this continuity of physical and vital action proceeded — 
by heterogeneous impulses or by correlated pulsations. If the 
latter, then the history of the earth, when deciphered, will 
assume a rhythmical periodicity susceptible of natural classifica- 
tion and of significant and rational nomenclature; if the former, 
the contradictory phases of local actions will inhibit all but the 
most general unity and render classification and nomenclature 
either arbitrary or provincial. 
I venture to urge three general grounds upon which I enter- 
tain the former view. These grounds, if valid, hold out the 
hope that the history of the earth will be found not only sus- 
ceptible to natural division, but capable of its truest exposition 
only through the recognition of its inherent periods. 
I. The first of these grounds is the presumption that great 
earth movements affect all quarters of the globe. Minor 
stresses may find relief in local readjustment, but profound 
stresses cannot be relieved, it is assumed, without generating 
appreciable stresses in other portions of the globe and leading 
to general readjustment. In a globe, all of whose parts owe 
their positions to the stress and tension of other parts, every 
rearrangement that rises in magnitude above the limits of local 
support extends its influence to the whole. Any massive earth 
movement must change the gravitative stresses of all parts of 
the globe unless the movement be divided into contrary phases 
so adjusted as to be compensatory, the possibility of which in 
the strict sense may be questioned. The recognized causes of 
profound movements such as secular refrigeration, change of 
speed of rotation, progressive molecular rearrangement, and like 
agencies, are comprehensive in their action and accumulate 
general stresses whose natural issue is coéperation in a common 
movement of relief. 
