46 
VOLCANIC CHRONOLOGY 
BOOK 1 
Another well-known region of modern Puys is that of the Eifel, where 
the cones and craters are often so fresh that it is difficult to believe them 
to be prehistoric^ One of the most remarkable denuded puy-regions in 
Europe covers a wide territory in the Swabian Alps of Wtirtemberg. No 
fewer than 125 denuded necks filled with tuff, agglomerate and basalt have 
there been mapped and described. They are of higher antiquity than the 
Tipper Miocene strata, and have thus probably been exposed to prolonged 
denudation. In external a,spect and internal structure they present the 
closest parallel to the Carboniferous and Permian “necks ” of Britain described 
in Books VI. and VI 1. of the present work." 
Among the Pakcozoic volcanoes of Britain many admirable illustrations 
of the Puy type are to be found. Their cones are almost always entirely 
gone, though traces of them occasionally appeal-. The “ necks ” that show the 
position of the vents are in some districts crowded together as thickly as 
those of Auvergne. During the Carboniferous and Permian periods in 
Central Scotland, clusters of such little volcanoes must have risen among 
shallow lagoons and inland sheets of w-ater, casting out their ashes and 
pouring forth their little streams of lava over the water-bottom around them 
and then dying out. As these eruptions took place in a region that 
was gradually subsiding, the cones and their ejected ashes and lava.s 
were one by one submei-ged, the looser materials being washed down and 
spread out among the silt, sand or mud, and enveloping the remains of any 
plants or animals that might be strewn over the floor of the lake or sea. 
Hence the Puys of Paheozoic time in Britain have been preserved with 
extraordinary fulness of detail. They have been dissected by denudation, 
both among the hills of the interior and along the margin of the sea. Their 
structure can thus be in some respects made out even more satisfactorily 
than that of the much younger and more perfect cones of Central France. 
iv. DETERMINATION OF THE RELATIVE UEOLOGICAL DATES OF ANCIENT 
VOLCANOES 
In themselves, accumulation.s of volcanic materials do not furnish any 
exact or reliable evidence of the geological period in which they were 
erupted. The lavas of the early Palieozoic ages may, indeed, on careful 
examination, be distinguished from those of Tertiary date, but, as w'e have 
seen, the difference is rather due to the effects of age and gradual alteration 
than to any inherent fundamental distinction between them. In all essential 
particulars of composition and internal structure, the lavas of the Cambrian 
or Silurian period resemble those of Tertiary and modern volcanoes. The 
Ventral Frmiee, 1858 ; Leoiwps jijwqncs Giologiqucs de V Av.rergnc, 1867 ; M. Michel Levy, BnlL 
Roc. Oiol. France, 1890, p. 688 ; iM. Honle, Ihill. Va.rte lUol. France, No. 28, tome iv. 1892. 
' Tile Eifel district lias lieoii fully deswibed by llibbert. Von Decheii, and other writers. You 
Uecheu’s little handbooks to the Eifel and Siebengebirge are useful guides. 
These Wilrtomberg vent.s have been elaborately described and discussed by Professor VV. 
Hraiico of Tubingen in his Rchwahens 7^7 Vulkan-Eiiihnjoneti vnd dcren tufe.rfuUc Ansbruche- 
ruhren, das grOssle (lebiel ehcnutligcr Aaare anf der Frdc, Stuttgart, 1894. 
