Geology of Tcviiincrfors. — Scderlwlm. 2 1 3 
we do not believe that these pegmatytes bear the same rela- 
tion to the granite that is usually attributed to the aplyte and 
lamprophyre dikes which represent the last differentiation 
products of the granite magma. The word "dike" here used 
for these pegmatytes is perhaps inaccurate if used in the 
genetic sense of an igneous intrusion. The pegmatytes cut- 
ting the gneiss are more like quartz-feldspar "veins," varying 
from a few inches to two feet in width, sometimes drusy, show- 
ing idiomorphic terminations to the crystals in open cavities, 
sometimes an aggregate of granular quartz with. very little 
of the feldspar. Elsewhere the "graphic granite" structure 
predominates. Were it not for these feldspathic intergrowths, 
the word "vein" would both here and in the intrusions in the 
diabase seem more appropriate. In both cases it is believed 
that the deposits were made from super-heated waters under 
pressure, which took into solution from the rocks through 
which they passed (probably largely granite) the necessary 
mineral matter. The period at which this took place was after 
the consolidation of the Medford diabase intrusions, probably 
post-Mesozoic. This is proven by the zonar growth of the 
feldspars of the so-called quartz-diabase, by the pegmatyte 
veinlets and by the secondary pegmatyte bands surrounding 
the quartz inclusions. We thus conclude that granophyric in- 
tergrowth of quartz and feldspar in a diabase is not necessarily 
evidence of the primary nature of these minerals. 
THE GEOLOGY OF THE ENVIRONS 
OF TAMMERFORS. 
By J. J. Sederhol.m. 
[Traoslatecl from the (juifle to tlio excursions of tla- Seventh International Con- 
f?ress of Geologists.] 
The Archean rocks of the envirc^iis of Tanimerfors can 
be divided into tliree parts which are as follows from above 
downward. 
1. Post-Bothnian j^ranite. 
2. Bothnian schists. 
3. Pre-Bothnian terrane of gneiss. 
In the last, granites, which are essentially metamorphic, 
prevail, in part porphyroids, and foliated gneisses which are 
