Formaton of Continents and Oceanic depressions. 167 
4, Change of density and volume in solidification. 
All the rocks above mentioned have a higher density in 
the solid state than when in fusion. According to Delesse,* 
9; diorite, 6 to 8; dolerite and melaphyre, 5 to 7; basalt and 
trachyte 8 to 5 per cent. The difference in volume is thus 
large between a rock in the solid and glass state. As to the 
difference between the glass and liquid states we have no pre- 
earing rocks from the crust, and, therefore, of granite or 
syenite, and the other considerations presented, we may take 8 
per cent as the probable average change of density for the 
earth’s crust between the stony and the liquid states; which 
adjoining would have continued to flow over the solidifying 
area and add to the solidifying material. 
* Bull. Soc. Geol. de France, II, iv, 1380, 1847. Delesse's results agree nearly 
with those of St. Claire Deville. Bischof in 1841 found the volume of basalt in the 
vitreous and crystalline states as 1 to 0°9298; for the same, © the fluid and crys- 
OREO as 1 to 0°8960; and for granite, the corresponding ratios, 1 to 0°8420, 
tIt is to be here noted that the glass and stone conditions are distinct molecular 
States o: same substance, the former produced under rapid cooling, 105 69 
under slow; and that common glass will become stone if solidified under @ pro- 
longed cooling process. : 
tI am informed that at the Lenox Glass Furnace in Berkshire, Mass., n0 con- 
traction is noticed in the cooling of the glass. 
