680 On the Evidence that the Earth's Interior is Solid. Cl, 
crust has formed upon the surface; and furthermore, that the 
crust always remains upon the surface and does not sink.” 
He also remarked that “a crust of the specific gravity of 265 
cannot sink deep down into the fluid mass of a globe possessing | 
the mean density of 5.3.” , 
In looking over the data for the assumed contraction of thè 
materials forming such portions of the earth’s crust as we ar- 
able to examine, it will be seen that the early experiments of 
Bischof indicated a contraction in passing from the liquid to the 
crystalline state for basalt of some ten per cent, of trachyte 
eighteen per cent, and of granite twenty-five per cent; or tabu- 
lating the results, we obtain, according to David Forbes? 
4 
f 
hea o Glass. Crystalin, 
TA ass eens N ee 1000 963 w 
Trachyte E T T 1000 888 818 
ET P De E A E T eee 1000 888 148 
cooling, 
The question of the contraction of igneous rocks in 1% 
was further taken up by David Forbes,’ although none m 
observations appear to lead to any more definite cma 
that Bischot’s results were much too high, and that his w , 
too crude to be of any great value. ag 
In a later paper Forbes pointed out that in nature par | 
evidence of a contraction of from one-tenth to ont se d 
volume, such as Bischof had held, when the rocks in 
dikes, etc., were studied 7” situ—a statement that 
petrologist will sustain.* > aicen OF 
Some further experiments on the contraction ea ned tot 
terials in cooling were made by Robert Mallet. erat 
“that the difference in specific acude 
the result showed a seen red ok tne “a 
na 
SeN: 
TAr Fa 
, : +a crust 
admit of a thin or a thick terrestrial pores oe th 
ported by and upon the surface of the liquid & i 
r il ere 
1 Geol. Mag., 1867 (1), IV, 431-4445 Chemical News, 1868, 
110-113. r 
2 Neues Jahr. Min., 1841, pp. 565, 5675 1843. pp. 1-54 
XVIII, 191-1 
3 Chemical News, 1868, XVIII, 191-194. 
4 Geol. Mag., 1870 (1), V11, I~4- 
tion which intervenes between the peing pi 
