Review of Recent Geological Literature. 119 
tation from E.D. Preston : "Nothing is more in accordance with 
the action of physical laws than that the earth is contracting in 
approximately a tetrahedral form. Given a collapsing homo- 
geneous spherical envelope, it will assume that regular shape 
which most readily disposes of the excess of its surface di- 
mensions ; or, in other words, the shape that most easily relieves 
the tangential strains ; for, while the sphere is of all geometric- 
al bodies the one with a minimum surface for a given capacity, 
the tetrahedron gives a maximum surface for the same condi- 
tion. Experiments on iron tubes, on gas-bubbles rising in 
water, and on rubber balloons, all tend to bear out the assump- 
tioii that a homogeneous sphere tends to contract into a tetra- 
hedron." 
iTo be continued.) 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Jovellania triangularis ini Mitteldevon der Eifel, von E. Kayser (Cen- 
tralblatt fiir Mineralogie etc., 1900, p. 117.) 
The occurrence of this well known Devonian species of Archaic in 
loose fragments along with a characteristic middle Devonian fauna at 
Lissengen in the Eifel is described. G. f. m. 
A brief review of the titaniferous magnetites. By J. F. Kemp. (School 
of Mines Quarterly, 20. 323-356; 21, 56-65.) 
The known deposits of magnetic iron ore may be conveniently clas- 
sified into two groups on the basis of chemical composition ; the titan- 
iferous and the non-titniferous. This grouping not only corresponds to 
the chemical composition, but also to the geological relations and to the 
present utilization and non-utilization. 
Among the magnetic ores the non-titaniferous are today the only 
ones mined and smelted and even their productiveness has decreased 
notably in recent years, because of the great influx of cheap and easily 
reduced hematites from lake Superior. The Cornwall banks in Penn- 
sylvania are almost the only large American magnetite mines now in 
active operation. The geological relations of the non-titaniferous ores 
are variable, and, in one place and another, they have resulted from very 
different originals and by strongly contrasted processes, but if titanif- 
erous iron sands are omitted, the massive titaniferous ore-bodies may 
be said to be closely allied in character and origin wherever they have 
been studied. With one or two exceptions the titaniferous magfietites 
are associated, so far as known, with rocks of the gabbro family and 
