736 
down, and whilst it has disappeared everywhere else in the neigh- 
bourhood by erosion, we see the remains preserved just on these 
spots where the roof has given way. 
Consequently the massive of the Pilandsbergen does not belong 
to that important class of intrusions, to which tangential pressure 
in the portion of the eartherust in which the intrusion takes place 
is necessarily connected, which is proved moreover by the existence 
of a great number of vertical dykes of vast extension. Blocks 
sinking elsewhere cannot have been the cause of the intrusion 
of the magma, as the roof has sunk down exactly on those 
spots, where the foyaitie magma has risen. Certainly pressure and 
faults are directly connected with the mechanism of the older chief 
intrusion of the Boschveld 5, and also the young foyaitic intrusions 
are chiefly restricted to those spots where tension has taken place, 
and consequently the pressure has been diminished. 
Thus both the sinking down of the roof and the intrusion are 
regarded as consequences of the same common cause, which occasioned 
the relief of pressure; the question in how far the sinking down of 
fragments of the roof into the magma underneath has contributed so 
the batholitie invasion (DaLy’s “overhead stoping’’) is in this respect 
of secondary importance ; we must however admit that sinking down 
and intrusion took place partly simultaneously. 
Similar conditions are found likewise in the Greenland rocks. 
Formation of the schistose stuctures. 
The formation of these structures in consequence of flow in the 
crystallizing magma is improbable for the following reasons: 
1. For a great vertical distance the direction of the plane of schis- 
tosity by parallel-structure remains the same. Consequently we should 
have to admit in a batholite for a considerable height a gradual 
decrease of rapidity in the flowing magma. Ramsay has already pointed 
out the improbability of this theory. 
2. The aegirine-needles lie for the greater part parallel to the plan 
of schistosity but in it they are irregularly distributed. In a flowing 
magma the needles would have a tendency to arrange themselves 
parallel to the direction of the flow. Indications of such an arrangement 
are missing. 
3. The lujaurites vary and by transitions are connected with other 
rocks without parallel structure. If we admit flow-structure, then other 
1) G. A. F. MoLeNGRAAFF, Geology of the Transvaal. Johannesburg 1904, p. 50 
sqq. A. L. Haut, Ueber die Kontaktmetamorphose an dem cba amit ie im 
östlichen und zentralen Transvaal. Min. u. Petr. Mitt. XXVIII, Heft 1, 2, 1909. 
