Origin of the Grand Outline Features of the Earth. 393 
of crystalline grains; though theie may be also other independent 
lines of fracture. here is abundant evidence of a uniformity of 
cleavage direction in the coke of the surface over large areas, as 
already explained. Such a cause would have acted more uni- 
formly at the first cooling of the surface, when from the previous 
free liquidity, the material was more uniform in character than at 
any time afterward : and even though the material were different in 
different parts, it matters little, since feldspar is common in almost 
every igneous rock, and is a frequent source of cleavage in two 
directions at right angles with. one another, independently of 
the foliation an ae mica and hornblend when either of these 
minerals are pre 
_M. Necker, in a article already alluded to, suggests that the 
trends of mountains, coast lines, and the strike of strata, we 
With magnetic curves. The same cause is appealed to by Boa: 
la Beche, on the ground that the electrical currents ats 
ersing the globe may influence the polar forces of crystallization. 
It has since been demonstrated by Mr. R. Hunt that the direction 
of crystallization is influenced by magnetism,t and R. W. Fox 
had before shown the action of elacineal forces in a 
dies, aia with lines on his chart. .'The exceptions are’ many 
and look insurmountable ; but they are to some extent remov: 
bya knowledge of other sources of influence. It should also 
be remembered that lines of magnetic intensity, as Brewster has 
shown, correspond. nearly with isothermal lines; and the two 
agencies, heat and magnetism, must therefore have acted in some 
degree ees at all periods.$ 
_ Hop his able “Researches on Physical Geologyy "i 
(1835, i the regularity of joints in rocks to the m 
leal action of an elevating force, and he establishes a perfect uni- 
* Treatise on Primary Geology, by H.S. Boase, M. D.; 8vo, Lonigms 1sd4,and 
mand EP Phil. Mag., and 26ut,,°, vile 4; x, 14. : i 
t Phil. Mag., Jan., 1846, p. 1; Amer. Jo sat: Sci, - Ser., ii, 116. 
$3 mes of the Polytechnic ‘Soriety of Comet e or 1837, pp- 20. 21 ae im- 
gin ¥ :_ Sans-avoir besoin de sapposer Mieke os ses alt : babies 
ent un cristal, it suffit de lui accorder ae n ggibnng tae intérieures — 
ec Lode de 
forces centrifuge et centripete. Ceci on en doit déduire necessairement 
les premieres me cupé Jes parties du spheroid les plus ace identées, a 
taines grandes chaines offrant encore Jes de ces formes réguliéres, us 
do-réguliéres et puisque ces s¢ries de montagnes constituent l’ossature des conti- 
hents, et déterminent leur figure, on “voit de nouveau combien la similitude des 
continents éclaire U’etude pour ains dirg eitallgrap aphique du noyau terrestre. Bull. 
la Soc. Geol. de France, i, ii Ser., 355. 
falar Camb. Phil. Soc., vii, l- 
D Serizs, Vol. Ill, No. 9.—May, 1647. 50 
