258 Rev. O. Fisher—Thickness of Marine Deposits. 
that the mean temperature of the whole column will be raised, and 
it will expand. This expansion, however, will not alter its weight, 
so that it will continue to float with its base still immersed at the 
same depth in the substratum as before expansion began. The head 
of the column would consequently rise above the sea-level, and con- 
tribute its share towards the formation of an elevated plateau. It is 
obvious that the supposition we have made that the flow of heat is 
held in abeyance will give the height of the plateau too great, because 
the column will really begin to swell upwards immediately that the 
blanketing by the deposit commences, and the sea-level will be 
reached, and deposition cease, sooner in nature than in the case 
supposed, because what would actually happen would be, that when 
the deposit had attained such a thickness that the expansion going 
on during its deposition had brought it up to the top of the water, 
then no more could be deposited, and it would be only the balance 
of heat due after that, to make the flow steady and the gradient 
equable, which would be actually efficient to raise a plateau. In 
fact, if the rate of deposition were sufficiently slow, it is conceivable 
that no plateau at all might be formed, the sea being just filled up 
by the expanded column. It seems therefore probable that coarse 
deposits, which are more rapidly accumulated, might be raised into 
higher plateaus than finer ones. 
To obtain the alteration in volume due to the expansion, we 
require to know the melting point of the substratum, and also the 
coefficient of expansion of rock. Dr. Carl Barus found the melting 
temperature of Diabase to be about 1100°CU. or 2012°F.; while 
Professors Riicker and Roberts-Austen have determined that of the 
Basalt of Rowley Regis to be about 920°C. or 1688°F.’ We shall 
not be very far wrong therefore if we put the temperature of the 
substratum at 2000°F. The coefficient of the expansion of rock 
has been investigated by several experimenters, and for the voluminal 
expansion may be taken as 0-:0000215 for 1° Fahr. 
In the appended note a simple expression is found for the 
voluminal expansion of the column, consisting of the new deposit 
and the old crust, after the flow of heat has become steady and the 
gradient again equable. In the first case examined, when there is 
no melting off at the bottom of the old crust, the expansion would 
be 0:09 of the original depth of the sea. Thus, if the sea were a 
mile deep, the expansion of the column would be 475 feet. 
In the second case, where the thickness of the deposit and what 
remains unmelted of the original crust is supposed equal to the 
original thickness of the crust (which seems probable), the expansion 
has been found in terms of that thickness and the depth of the sea. 
Thus, if the crust were twenty miles thick, and the original depth of 
the sea were one mile, the expansion of the column after the sea 
was filled up would be 1800 feet. 
The amounts of expansion obtained here are voluminal. And con- 
sidering that lateral expansion would be prevented by the adjacent 
1 See ‘‘ Appendix to Physics of the Earth’s Crust,’’ p. 19. 
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