Rev. O. Fisher—Thickness of Marine Deposits. 261 
If we make the second supposition, that the deposit and the 
unmelted crust maintain the original thickness of the crust, since 
s—m 
pops, it appears that the greatest thickness of deposit will 
be 10-9 times the original depth of the sea. These estimates are 
necessarily affected by the uncertainty which attends the know- 
ledge of the relative densities. If, for instance, the densities of the 
crust and substratum are more nearly equal than we have assumed 
them to be, the possible thickness of deposit in this latter case 
would be greater. 
To find the rise of temperature in the column of the crust and the 
deposit, and the resulting voluminal expansion. 
(Fie. 2.) 
Let AK=Z£ be the original thickness of the crust, AB=y the 
thickness of the deposit and let KC represent the melting tempera- 
ture é at the bottom of the crust. Then AC will be the temperature 
gradient at first. 
_ After the deposit has been laid down, and sufficient time elapsed 
for the flow to have again become steady, suppose KK'=k—K’ to be 
the thickness which has been melted off the bottom of the crust. 
Draw K’C’=KC’=t and then BC’ will be the final temperature 
gradient. 
If we draw lines as m n parallel to K’C’ these will represent the 
increase of temperature at each depth, and the elementary area, 
representing the product of any such line with the mcrement of 
depth, will represent the product of the increase of temperature into 
the increment of volume of the column of unit sectional area; and 
this, multiplied by the coefficient of voluminal expansion H#, will 
give the expansion of that element of the column. Hence Hx the 
sum of such elementary areas will give the expansion of the whole 
column: that is 
Expansion of the column = EH x area BA QC 
= H(BK'C—A K’Q) 
= E(RBKxK' C'-34K'xE' Q) 
ki 
— ay / ae as geen ; 
— EF G Y+H)t—ghe t ) 
12 
=E(yt¥—-")< @) 
If we suppose that there is no melting off at the bottom of the 
t 
x" 
Taking H = 0-0000215, y= 4 26d, and ¢ = 2000° F., we obtain 
for the expansion of the column 0-09 d; so that, if the sea was a 
mile deep, the expansion of the column subsequently to the sea being 
filled up would be 473 feet. 
If we make the supposition that the thickness of the crust which 
crust, then k’ and & are equal, and the expansion becomes E y 
