GENESIS OF THE ALKALINE ROCKS 103 
in the sill and laccolith chambers and finally crystallized as nephelite 
syenite and its by-products. 
The crescentic laccolith near Tory Hill illustrates gravitative 
differentiation, also well displayed in several other of the thicker 
alkaline bodies. The maximum thickness of the laccolith is only 
about three hundred feet, yet it shows a striking variation from 
top to bottom as here indicated: 
a) Pegmatitic nephelite syenite, with specific gravity of 2.674; 
carries microperthite (59 per cent), nephelite (2t per cent), and 
albite (12 per cent); contacts with limestone roof. 
b) Monmouthite, with specific gravity of 2.719; carries 
nephelite (57 per cent), albite (9 per cent), scapolite (ro per cent), 
and biotite (22 per cent). 
c) Hornblende-nephelite rock, with specific gravity of 3.124; 
carries nephelite (30 per cent), albite (7 per cent), pyroxene (20 per 
cent), hornblende (30 per cent), garnet (7 per cent), and primary 
calcite (5 per cent). 
d) Garnet-pyroxene rock, with specific gravity of 3.383; carries 
albite (3 per cent), pyroxene (34 per cent), garnet (37 per cent), 
and primary calcite (25 per cent); contacts with limestone 
OL. 
~ The mineralogical composition of the Tory Hill and other 
laccoliths of the district directly indicates the probability of syntexis 
between magma and limestone. Of course there is no necessity of 
assuming that all, or even the larger part, of this assimilation took 
place at the visible contacts. 
Palingenesis in relation to the problem.—Basaltic magma may 
not at all have participated in these Ontario developments. The 
writer suspects that, like many other pre-Cambrian invasions of 
magma, the petrogenic cycle was not opened by the abyssal injec- 
tion of basalt. Along with Lawson, Sederholm, and other workers 
in pre-Cambrian complexes, one is rather tempted to regard the 
activity of the granite magma as due to palingenesis, that is, 
‘refusion of the crustal granite at a level not far below that to which 
erosion has brought the general surface of Haliburton County. 
This whole field exemplifies the difficulty of applying to the granites 
of the older pre-Cambrian terranes any petrogenic scheme that 
