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APRIL 25, 1884. ] 
should be a system of them reaching to every 
part of the vessel ; for the pumps may be needed 
the most when the vessel is careened on her 
beam, or at some unusual angle fore and aft. 
If possible, a tender should accompany the 
exploring-vessel proper, especially if she be a 
steamer, whose stores of coal and other articles 
are to be transferred when the ice becomes 
dangerous for such a craft, presumably not 
strengthened to combat with that element. 
FREDERICK SCHWATKA. 
ON THE FUNDAMENTAL THEORY OF 
DYNAMIC GEOLOGY. 
Many lines of inductive research lead to the 
conclusion that the interior of the earth is ina 
fluid condition, and that the solid shell is com- 
paratively very thin, but variable in its thick- 
ness from district to district, and in the same 
district from time to time geologically. A 
crust twenty-five miles in thickness at a maxi- 
mum, and very much thinner at a minimum, best 
explains geologic phenomena. If we consider 
this crust to be made up of units defined at the 
upper surface by districts of some magnitude, 
it seems necessary to regard it as existing ina 
state of floating equilibrium; so that, if some 
portion of the rocky material is taken from any 
such district, it rises, and the district on which 
it is deposited subsides. In case material is 
transferred for a very short distance, appre- 
ciable displacement may not result, the local 
structural rigidity being sufficient to withstand, 
or largely withstand, the stress. But if the 
short transferrence is across the line of a fault, 
from the upraised to the thrown side, the facts 
seem to show that the upheaved side continues 
to rise by reason of unloading, and the thrown 
side to subside by reason of increased load. 
The rigidity of the crust of the earth arising 
from the molecular cohesion of the solid state 
is greatly modified by mechanical structure. 
The crust is composed of geologic formations 
of diverse origin, diversely arranged. The for- 
mations are broken into great blocks by great 
fault and flexure planes, in many cases doubt- 
less extending quite through the crust. It is 
also fractured in multitudinous ways, and the 
crevices filled with vein matter. Again: each 
block or segment of a faulted formation is di- 
vided into small fragments by stratum planes, 
joints, schist planes, and slaty cleavage. The 
rigidity of each minute fragment is due to the 
molecular cohesion of solidity. but the general 
rigidity of the crust is dependent on mechani- 
SCIENCE. 
11 
cal structure. ‘The fragments of which the 
crust of the earth is composed are exceedingly 
minute when compared with geologic forma- 
tions, and they appear relatively as but grains 
of sand when compared with the whole crust 
of the earth. 
This fragmental character of the crust is 
exhibited at the surface, and to the greatest 
depths to which observation has extended ; and, 
so far as it depends upon the great faults, it 
must extend quite through the crust. There 
may be and probably is a zone beneath, so 
nearly fluid by reason of temperature and 
pressure, that fractures are less easily gener- 
ated and more easily repaired, but the rigidity 
of the crust is not increased thereby. 
The solidity of the crust of the earth is lim- 
ited by temperature and pressure under condi- 
tions of chemical constitution and hydration, 
and is further limited by the conditions of its 
mechanical structure. 
If vertical stress be applied to a point on 
the surface of the earth, the strain is propa- 
gated laterally by the condition of rigidity, but 
not indefinitely, as this rigidity speedily van- 
ishes in the presence of the enormous forces 
involved in the weight of the crust itself, and 
in the great bodies of matter that are unloaded 
and loaded at the surface. ‘The distance to 
which the strain extends is greatly lessened by 
the fact that the crust is not a continuous solid 
by cohesion, but preserves continuous rigidity 
in a very imperfect way by mechanical struc- 
ture alone. 
If the crust of the earth were practically ho- 
mogeneous in the specific gravity of its mate- 
rials, its static equilibrium would not permit 
the existence of any great elevations at the 
surface; but to the conclusion of a general 
equilibrium, geologists and geodesists are alike 
converging ; and, if true, it necessitates the fur- 
ther conclusion that the crust, and perhaps to 
some extent the underlying fluid matter, is of 
varying density from region to region. This 
conclusion follows from a consideration of the 
inequalities of altitude existing in the earth’s 
surface : and, since they are ever changing from 
district to district, —as one subsides and an- 
other rises, — contraction and expansion must 
occur. The necessity for the hypothesis of 
contraction and expansion is not obviated by 
the hypothesis of a fluid interior, nor is the 
latter rendered unnecessary by the former. 
There is a constant lateral transferrence of 
material at the surface by rains, rivers, and 
marine currents; there is a constant verti- 
cal transferrence of material by displacement ; 
there is a constant transferrence of material 
