226 The American. Geologist. April, i898 
stated to consist of dioryte and peridotyte. This pre-Both- 
nian gneiss and the schists which accompany it are com- 
parable to the gneiss and schists of the Lower Keewatin when 
crystaUine, to which Lawson gave, in part at least, the name 
Contchiching, and the intersecting granites when intrusive to 
Ihe earliest Minnesota granites. 
To the north from this belt of strongly metamorphic and 
highly folded rocks is a great formation which Sederholm has 
named the schists of Tammerfors, or the Bothnian formation, 
which lies in discordance of stratification on the foregoing. 
This consists of detrital matter, showing distinct sedimentary 
structure, and developing a thickness of four to five thousand 
metres. Its beds are nearly or quite vertical, and while 
plainly of fragmental nature they are also distinctly crystalline. 
They are phyllytes which approach argillytes and sometimes 
pass into a fine-grained mica schist, and when they contain 
feldspar they present a gneissic character. But the most re- 
markable feature of the Bothnian formation is the prevalence 
of conglomerates. The pebbles vary from microscopic grains 
to half a metre in diameter. They are well rounded, the 
greater part consisting of different porphyritic effusives, but 
there are also pebbles of porphyroids, phyllyte and leptyte. 
This conglomerate has a crystalline cement, and, along with 
the phyllytes it is converted into mica schists. The forms of 
the boulders are most distinctly outlined on weathered sur- 
faces, but when freshly broken they are so intimately blended 
with the cement that it is impossible to distinguish their limits: 
except that, frequently, the secondary feldspars are more pro- 
fusely or more sparingly developed in the boulders than in the 
rest of the rock surrounding. The beds of conglomerate al- 
ternate with a dark green schist, which, according to Seder- 
holm, is a metamorphic volcanic tuff, cotemporary with 
the conglomerates. The Bothnian formation seems to par- 
allelize well with the Upper Keewatin of Minnesota, both pet- 
rographically and structurally. 
The latest granitic invasion in Finland, as described by 
Sederholnr in the guide-book of the excursions of the 
Seventh International Congress of Geologists, is that which 
cuts the Bothnian formation. The earlier granite, and the 
earlier schists associated with it, are found in fragments in the 
