THE OLDEST MOUNTAIN IN ENGLAND. 
17 
stone.” Greenstone is a dark crystalline volcanic rock, poor in 
silica, and characterised by the large proportion of iron, mag- 
nesia, and lime contained in it. But the Wrekin is chiefly 
composed of rocks of a pink, red, or grey colour, rich in silica, 
and deficient or wanting in iron, lime, and magnesia. This 
rock, so far from being disruptive, was deposited in beds not 
only before the Caradoc epoch, but long anterior to the much older 
Cambrian strata. Let us examine these points in more detail. 
In modern volcanic eruptions the ejected matter is either 
felspathic or augitic. The latter is dark coloured, and contains 
a large proportion of the bases named as characterising green- 
stone ; indeed, we may consider augitic lavas as the modern 
representatives of the ancient greenstones. The felspathic 
ejections of volcanoes are either molten as lava-flows, or frag- 
mental as ashes and breccias. They are generally lighter in 
colour, and, containing less iron, are not so heavy. No essential 
distinction can be made between ancient and modern igneous 
rocks. Both are the result of the same heat forces. In all 
ages volcanic action has been ejecting ashes, pouring forth 
floods of molten lava, and injecting into fissures of the crust 
melted matter which cannot reach the surface as lava. Beds 
of ashes, layers of lava, amorphous masses of molten rock, 
the common products of Etna and Vesuvius, were formed in all 
geological epochs. The separation of igneous rocks into vol- 
canic or modern, and plutonic or ancient, is arbitrary and unphi- 
losophical, and is furthermore calculated to mislead the student 
by suggesting that plutonic rocks were formed under mysterious 
and unknown conditions. Mr. Allport has shown, by both 
chemical and microscopic analysis, that the rocks of the Wrekin 
are identical with the modern ejectamenta of volcanoes. Certain 
changes have taken place during the lapse of ages by the action 
of infiltrated atmospheric waters, but it cannot be doubted that 
originally the volcanic rocks of the Wrekin were essentially the 
same in composition and in mode of formation as the materials 
of modern volcanoes. This is one of the most important gene- 
ralisations of recent years, and it derives additional interest 
from the discovery by the writer of the Pre-Cambrian age of 
the Wrekin. Mr. Allport carried back the period of existing 
volcanic action to what he considered Silurian times. In this 
paper it will be shown that in times perhaps more remote from 
the Silurian than the Silurian is from ours, the volcanoes of 
Shropshire ejected lava and ashes undistinguishable from the 
products of existing craters. The fire forces may have been 
more energetic, but they produced the same results in the same 
way. The volcanoes which in Pre-Cambrian times covered with 
their lavas and ashes the area now called South Shropshire were 
NEW SERIES, VOL. III. — NO. IX. C 
