PAGE 2nd BRANCH OF THE INQUIRY, viz. General inferences with reference to the connection The greater compactness of Trap Rocks accounted for.. 397 .... Why submarine Lavas have cooled slowly.. Differences between Trap and Volcanic Rocks shewn Ejected through the medium of dykes.. Changes produced by these on the surfaces of the con- Distinctions in character between the products of Vol- canic action at this and at later periods... LECTURES ON VOLCANOS. LECTURE I. ON THE VOLCANOS OF FRANCE AND GERMANY. Introductory remarks.-Volcanos when to be considered active-when extinct-Characters by which the latter may be known-Classification of Volcanic products according to their Mineralogical constitution. Extinct Volcanos of France-In Auvergne two classesPost-diluvial and Ante-diluvial—the former class considered their antiquity.—Problematical Rock of the Puy de Dome, &c.-Mode of its formation discussed.Second Class of Volcanic Rocks-1st, near Clermont, where they consist of Tuffs alternating with Freshwater Limestones.-2d, at the Mont Dor-its Basaltic and Trachytic Formation considered-3d, in Cantal.-Volcanic Rocks of the Puy en Velay-of the Vivarais— their age.--Volcanic Rocks in other parts of France briefly considered. Volcanic Rocks of Germany-those near the Rhine-1st class, Post-diluvial.—Volcanos of the Eyfel-Crater of Laach-Lava of Niedermennig, Gerolstein, Mosenburg, Bertrich.-Trass of the Rhine considered-Whether the Post-diluvial Volcanos were in action since the existence A |