division. In west central Europe volcanic rocks are found at many
horizons, the most common rocks are diabases and diabase tuffs,
_schalstein_. Felsitic lavas and tuffs occur in the Middle Devonian of
Australia. Contemporaneous igneous rocks are generally absent in the
American Devonian, but in Nova Scotia and New Brunswick there appear to
be some.

There is little evidence as to the climate of this period, but it is
interesting to observe that local glacial conditions _may_ have existed
in places, as is suggested by the coarse conglomerate with striated
boulders in the upper Old Red of Scotland. On the other hand, the
prevalence of reef-building corals points to moderately warm
temperatures in the Middle Devonian seas.

The economic products of Devonian rocks are of some importance: in many
of the metamorphosed regions veins of tin, lead, copper, iron are
exploited, as in Cornwall, Devon, the Harz; in New Zealand, gold veins
occur. Anthracite of Devonian age is found in China and a little coal in
Germany, while the Upper Devonian is the chief source of oil and gas of
western Pennsylvania and south-western New York. In Ontario the middle
division is oil-bearing. Black phosphates are worked in central
Tennessee, and in England the marls of the "Old Red" are employed for
brick-making.

REFERENCES.--The literature of the Devonian rocks and fossils is very
extensive; important papers have been contributed by the following
geologists: J. Barrande, C. Barrois, F. Beclard, E. W. Benecke, L.
Beushausen, A. Champernowne, J. M. Clarke, Sir J. W. Dawson, A.
Denckmann, J. S. Diller, E. Dupont, F. Frech, J. Fournet, Sir A.
Geikie, G. Guerich, R. Hoernes, E. Kayser, C. and M. Koch, A. von
Koenen, Hugh Miller, D. P. Oehlert, C. S. Prosser, P. de Rouville, C.
Schuchert, T. Tschernyschew, E. O. Ulrich, W. A. E. Ussher, P. N.
Wenjukoff, G. F. Whidborne, J. F. Whiteaves and H. S. Williams.
Sedgwick and Murchison's original description appeared in the _Trans.
Geol. Soc._ (2nd series, vol. v., 1839). Good general accounts will be
found in Sir A. Geikie's _Text-Book of Geology_ (vol. ii., 4th ed.,
1903), in E. Kayser's _Lehrbuch der Geologie_ (vol. ii., 2nd ed.,
1902), and, for North America, in Chamberlin and Salisbury's _Geology_
(vol. ii., 1906). See the _Index to the Geological Magazine_
(1864-1903), and in subsequent annual volumes; _Geological Literature
added to the Geological Society's Library_