362 
magma. But with even a moderate viscousity there can be no 
separation of crystals by gravity, and although the crystallization 
may have been intermittent the consolidated rock will be uni- 
form in structure. Viscousity to some extent will also check 
the transmission of rapid variation in the pressure. 
ABSORPTION OF PRE-EXISTING ROCKS 
BY THE MAGMA. 
Hybrid nature of the soda-granite of Iviangusat. — The 
Paleozoic igneous rocks of South Greenland do not as a rule 
show any indications whatever which point to an assimilation 
of the wall rock. There are, however, some exceptions to this 
rule, and one of these is of special interest from a theoretical 
point of view. 
At the foot of the Iviangusat Mountains, in Kangerdluarsuk, 
the augite-syenite contains large and small fragments of sandstone, 
and these fragments are surrounded by a zone of soda-granite 
the width of which may vary from about half a meter up to 
two meters. The detailed geological and petrographical de- 
scriptions have been given in the preceding chapters (pp. 51 
and 116). The naked coast cliffs exhibit very fine sections in 
which the mutual relations of these rocks have been studied, 
and there can be no doubt that the soda-granite zones are root- 
less igneous rocks connected with the contact between sand- 
stone and augite-syenite. As most of the small fragments are 
well rounded it must be supposed that the magma has dis- 
solved sandstone, and there seems to be no escape from the 
conclusion that the soda-granile at this place is a hybrid rock’, 
and has originated by the assimilation of sandstone in the augite- 
! A. Harker, Natural History of Igneous Rocks, 1909, р. 333. _ 
