a 
eee 
“Parr L Sect iv.§1] HYPOGENE CHANGES. 291 
p- 298), and may even have been here and there enough for the actual 
fusion of the rocks by the crushing of which it was produced. 
Rise of temperature by intrusion of erupted rock.—The 
‘great heat of lava, even when examined at the surface of the earth, has 
been already referred to, and some examples have been given of its 
effects (p. 227). Where it does not reach the surface, but is injected 
into subterranean rents and passages, it must effect considerable 
changes upon the rocks with which it comesin contact. That such in- 
truded igneous rocks have sometimes melted down portions of the crust 
in their passage can hardly be doubted. But probably still more 
extensive changes may take place from the exceedingly slow rate of 
cooling of erupted masses, and the consequently vast period during 
which their heat is being conveyed through the adjacent rocks, 
Allusion will be made in later pages to the observed amount of such 
“contact metamorphism” (Book IV. Part VITI.). 
Expansion.—Rocks are dilated by heat. The extent to which 
_ this takes place has been measured with some precision for various 
kinds of rock, as shown in the subjoined table. 

Expansion for ‘ 
Rock. every 1° Fahr. Authority. 
Adie, Trans. Roy. Soc. Edin, xiii. 
Black marble, Galway, Ireland . | -00000247 { p. 366 
Grey granite, Aberdeen. . . . -00000438 | Ibid. 
Slate, Penrhyn, Wales. . . . | *00000576 | Ibid. 
White marble, Sicily . . . . | °00000613 | Ibid. 
Red sandstone, Portland, gan -00000963 
; Totten, Amer. Journ. Sct. xxii. 136. 
ticut 

According to these data the expansion of ordinary rocks ranges 
from about 2°47 to 9°63 millionths for 1° Fahr. Even ordinary 
daily and seasonal changes of temperature suffice to produce con- 
siderable superficial changes in rocks (see p. 319). The much higher 
temperatures to which rocks are exposed by subsidence within the 
eatth’s crust must have far greater effects. Some experiments by 
Pfaff in heating from an ordinary temperature up to a red heat, or 
about 1180° C., small columns of granite from the Fichtelgebirge, 
red porphyry from the Tyrol, and basalt from Auvergne, gave the 
expansion of the granite as 0:016808, of the porphyry 0-012718, of 
the basalt 0-01199'. The expansion and contraction of rocks by 
heating and cooling have been already referred to as possible 
sources of upheaval and depression (p. 284). 
Crystallization (Marble)—In the experiments of Sir James 
Hall, pounded chalk, hermetically enclosed in gun-barrels and 
exposed to the temperature of melting silver, was melted and 
partially crystallized, but still retained its carbonic acid. Chalk, 
1 Z. Deutsch. Geol. Ges. xxiv. p. 403. 
: u 2 
