54 
THE PERMIAN VOLCANOES 
BOOK VII 
generally unfossiliferous, though, when the conditions became more suitable, 
calcareous or dolomitic sediment accumulated on the bottom, to form what 
is now known as the “ Magnesian Limestone,” and muddy sediment was 
deposited which is now the “ Marl Slate.” In these less ferruginous strata, 
betokening a less noxious condition of water, various marine organisms are 
met with . 1 
The vegetation of the land surrounding these basins was still essen- 
tially I 'alamoic in character. It presented a general resemblance to that 
of Carboniferous time, but with some notable differences. The jungles of 
Sigillaria seem to have disappeared, while on the other hand, conifers 
increased in number and variety. The sediments of the water-basins have 
handed down only a scanty remnant of the animal life of the time. Along 
the sandy shores walked various amphibians which have left their footprints 
on the sand. A few genera of ganoid fishes have been found in some of 
the shales, and a comparatively poor assemblage of crinoids and molluscs 
lias been obtained from the Magnesian Limestone. To the geological period 
distinguished by these geographical and biological characters the name of 
Permian is assigned. 
In his survey of the progress of volcanic history in the area of Britain, 
the geologist finds that the long period of quiescence indicated by the deposi- 
tion of the Coal-measures, and probably also by the unconformability between 
the Coal-measures and the Permian formations, was at length terminated by 
a renewed volcanic outbreak, but on a singularly diminished scale and for a 
comparatively brief period of time. Whether, had the Permo-Carboniferous 
strata which connect the Coal-measures with the Permian formations on the 
Continent been found in this country, they would have filled up the gap in 
the geological record, and would have supplied any trace of contemporaneous 
volcanic action, cannot even be surmised. All that we know is that, after a 
vast interval, and during the deposition of the breccias and red sandstones 
which unconformably overlie the Coal-measures, a few scattered groups of 
little volcanoes appeared in the area of the British Isles. 
It is unfortunate that in those districts where these volcanic relics have 
been preserved, the stratigraphical record is singularly imperfect, and that on 
the eastern side of England, where this record is tolerably complete, there are 
no intercalated volcanic rocks. The latter occur in tracts where the strata 
are almost wholly destitute of fossils, and where therefore no palaeontological 
evidence is available definitely to fix the geological age of the eruptions. 
Nevertheless there is usually ample proof that the strata in question are 
much later than the Coal-measures, while their geological position and litho- 
logical characters link them with the undoubted Permian series of the north- 
east ol England. They may, however, belong to a comparatively late part 
of the Permian period, if indeed some of them may not be referable to the 
succeeding or Triassic period. 
1 In some recent borings around Hartlepool the Magnesian Limestone has been found to be 
iuterstratified with thick bands of gypsum and anhydrite, and to be overlain by more than 250 feet 
of the latter substance. Nothing could show more forcibly the exceedingly saline and insalubrious 
character of the Permian lakes or inland seas. 
