ORIGIN OF AMPHIBOLITES OF LAURENTIAN AREA 13 
scapolite having disappeared and a certain amount of biotite having 
been developed. 
A comparison of the analyses shows that the granite at first trans- 
fuses into the limestone, silica, alumina, oxides of iron and magnesia, 
with some alkalis and a small amount of titanic acid. As the altera- 
tion progresses, all these constituents continue to increase in amount. 
But in these later stages of the alteration the alumina, oxides of iron, 
and alkalis are added in relatively greater proportion than the other 
constituents, while no further addition of magnesia or lime takes 
place, the proportion of these constituents remaining essentially the 
same, the carbonic acid escaping and carrying the rest of the lime 
with it. 
This means, speaking generally, that pyroxene and some scapolite 
were first developed in the limestone and that later the feldspathic 
constituents increased in amount, the calcite present being removed 
in solution. 
A calculation of the analyses shows that Nos. 1 b and 2 have the 
following mineralogical composition: 
No. 10 No. 2 
HeldspathiciconStitwemtsi ssiielee) sei > i elaeeieead sa. 48.57 67.35 
Pyroxenic (iron magnesia) constituents........... 46.63 26.28 
TE OMMOTES pe sues teat ge Pastas des eshte acy aie o) ee oicerene Be2 5-27 
98.40 98. go 
NA TET Renter mannan ence aut ans armen cisbaCeh a brn mae ematical ova 1.66 I.00 
100.06 99.90 
During the change of No. 1 into No. 2 and this into No. 3, the 
information afforded by the analyses bears out that obtained from the 
study of the thin sections, showing that there has been a very con- 
siderable rearrangement among the constituents of the rock. ‘Thus 
it is seen that while the alumina and alkalis increase in No. 2 and 
No. 3, there is not a corresponding increase in the total amount of 
silica; the silica required to make additional feldspathic constituents 
being derived from some other reactions going forward in the rock. 
It seems also that after the development of a certain percentage 
of silicates in the limestone, as shown in No. 1, during which process 
