390 The American Geologist. December, 1903. 
with it before the intrusion took place, and were subsequently 
metamorphosed and recrystallized ; or they have been derived 
in some manner from the substance of the intrusive mass. The 
question resolves itself then into one of metamorphism by 
digenesis or by metasomatosis." 
The author gives no analyses of the limestones in their 
non-metamorphic condition, but assumes that they are "in 
general comparatively pure." He gives no analyses of the in- 
trusive granites, but he assumes that these substances have 
been introduced into the limestones by metasomatosis from the 
granites, and hence that, while the}' are distinctively banded, 
in the manner often regarded as sedimentary, the origin of the 
new substances as well as their' distribution in the limestone, 
date from the act of intrusion and are due to that intrusion — 
i. e. that the metamorphism is a species of extreme metasoma- 
tosis. 
To the reviewer the discussion seems to be a curious instance 
of arguing against a mass of adverse facts, and the alternative 
rejected is apparently more concordant with the facts than 
that which is accepted. The assumption that the limestone is 
comparatively pure away from the contact zone is gratuitous. 
It would be perhaps more reasonable to presume a priori that 
such impurities as "silica, alumina, iron, m? niesia, alkalies and 
chlorine ( for scapolite )"in the words of the author, existed pri- 
marily in an unanalvzed limestone rather than in an unanal- 
yzed granite, i.e. in quantities sufficient to give rise to the new 
minerals. There are also plain inferences from the facts given 
that the impurities mentioned were originally in the limestone. 
One or two may be stated, viz : calcite. which necessarily existed 
in the limestone in largest amount, diminishes toward the gran- 
ite. It is found in some amount still in the basic metamor- 
phosed zone : it is absent in the inclusions, and is not known 
in the granite. Again, scapolite, whose characteristic substance 
( chlorine ) is accepted as indicative of the origin of the im- 
purities, occurs in the metamorphic zone near the limestone, 
but the basic inclusions within the granite, having the same 
source as the metamorphosed zone, more remote from the 
limestone, do not contain it. and it is unknown to the granite 
proper. If these substances were derived from the granite by 
metasomatosis they should be found more abundant in the gran- 
