nt which has taken place in the strata. They
then show the phenomenon known as _slicken-sides_. Many faults have
become filled with crystalline minerals in the form of veins of ore,
deposited by infiltrating waters percolating through the natural
fissures.

In considering the formation and structure of the better-known
coal-bearing beds of the carboniferous age, we must not lose sight of the
fact that important beds of coal also occur in strata of much more recent
date. There are important coal-beds in India of Permian age. There are
coal-beds of Liassic age in South Hungary and in Texas, and of Jurassic
age in Virginia, as well as at Brora in Sutherlandshire; there are coals
of Cretaceous age in Moravia, and valuable Miocene Tertiary coals in
Hungary and the Austrian Alps.

Again, older than the true carboniferous age, are the Silurian
anthracites of Co. Cavan, and certain Norwegian coals, whilst in New
South Wales we are confronted with an assemblage of coal-bearing strata
which extend apparently from the Devonian into Mesozoic times.

Still, the age we have considered more closely has an unrivalled right to
the title, coal appearing there not merely as an occasional bed, but as a
marked characteristic of the formation.

The types of animal life which are found in this formation are varied,
and although naturally enough they do not excel in number, there are yet
sufficient varieties to show probabilities of the existence of many with
which we are unfamiliar. The highest forms yet found, show an advance as
compared with those from earlier formations, and exhibit amphibian
characteristics intermediate between the two great classes of fishes and
reptiles. Numerous specimens proper to the extinct order of
_labyrinthodontia_ have been arranged into at least a score of genera,
these having been drawn from the coal-measures of Newcastle, Edinburgh,
Kilkenny, Saaerbruck, Bavaria, Pennsylvania, and elsewhere. The
_Archegosaurus,_ which we have figured, and the _Anthracosaurus,_ are
forms which appear to have existed in great numbers in the swamps and
lakes of the age. The fish of the period belong almost entirely to the
ancient orders of the ganoids and placoids. Of the ganoids, the great
_megalichthys Hibberti_ ranges throughout the whole of the system.
Wonderful accumulations of fish remains are found at the base of the
system, in the bone-bed of the Bristol coal-field, as well as in a
similar bed at Armagh. Many fishes