295 
tolerably flat, and that its position may be approximately indi- 
cated as suggested in Fig. 26. 
Hypotheses to explain the mechanism of intrusion. — Since 
granitic and other abyssal rock bodies occupy a space which 
prior to the intrusion was occupied by the ‘country rock’, the 
intrusion must be preceded or accompanied by a removal of 
the latter rock. To explain this removal various hypotheses 
have been put forth. We will here discuss the question whether 
one or more of these hypotheses are applicable to the Ilimau- 
sak batholite. 
(L) In regions where moun- 
tain-making processes are going 
on, lateral thrust-movements may 
produce a subterranean cavity 
which is filled with magma con- 
currently with its formation (in- 
trusion by folding)’. In the Ili- 
mausak region no movements of 
this kind have occurred, and the 
Fig. 28. Map of the Ilimausak 
hypothesis, consequently, may be region showing position of sec- 
left out of consideration in the tions given in Fig. 27. — The 
closely dotted areas indicate the 
present case. batholitic rocks. 
(I) An empty space in the 
earth crust may be produced by volcanic outbursts of an ex- 
plosive character, and the cavity thus formed may be filled 
with magma. That this hypothesis which applies to a large 
number of ‘volcanic stocks’ is unable to account for the Ш- 
mausak batholite, is shown by the form of the cover and the 
large dimensions of this batholite. 
(IL) The pressure of the magma may have lifted the 
country rock from the space now occupied by the abyssal rock 
(laccolitic intrusion)”. Of late year several geologists have 
1 E. Suess, das Antlitz der Erde I, р. 218 (1885). 
2 W.C. BROGGER, die Eruptivgesteine des Kristianiagebietes II, р. 116 (1895). 
