Xiv CONTENTS. 



Strata altered at or near the contact — Obliteration of organic remains — Con- 

 version of chalk into marble — Trap interposed between strata — Columnar and 

 globular structure — Relation of trappean rocks to the products of active vol- 

 canoes — Form, external structure, and origin of volcanic mountains — Craters 

 and Calderas — Sandwich Islands — Lava flowing underground — Truncation of 

 cones — Javanese, calderas — Canary Islauds — Structure and origin of the Cal- 

 dera of Palma — Older and newer volcanic rocks in, unconformable — Aqueous 

 conglomerate in Palma — Hypothesis of upheaval considered — Slope on which 

 stony lavas may form — Extent and nature of aqueous erosion in Palma — Island 

 of St. Paul in the Indian Ocean — Peak of Teneriffe, and ruins of older cone — 

 Madeira — Its volcanic rocks, partly of marine, and partly of subaerial origin — 

 Central axis of eruptions — Varying dip of solid lavas near the axis, and further 

 from it — Leaf-bed, and fossil land-plants — Central valleys of Madeira not craters, 

 or calderas, - - - - - - - page 609 



Chapter XXX. — On the different Ages of the Volcanic Rocks. 



Tests of relative age of volcanic rocks — Tests by superposition and intrusion — 

 Test by alteration of rocks in contact — Test by organic remains — Test of age 

 by mineral character — Test by included fragments — Volcanic rocks of the Post- 

 Pliocene period — Basalt of the Bay of Trezza in Sicily — Post-Pliocene volcanic 

 rocks near Naples — Dikes of Somma, - - - - - 655 



Chapter XXXI. — On the different Ages of the Volcanic Hocks, continued. 



Volcanic rocks of the Newer Pliocene period — Val di Noto — Sicilian dikes — Region 

 of Olot in Catalonia — Volcanic rocks of the Older Pliocene period — Tuscany — 

 Rome — Volcanic region of Olot in Catalonia — 'Cones and lava-currents — Ravines 

 and ancient gravel-beds — Jets of air called Bufadors — Age of the Catalonian 

 volcanoes — Upper Miocene period — Volcanic archipelagoes of Madeira, the Ca- 

 naries, and the Azores — Lower Miocene period — Brown-coal of the Eifel and 

 contemporaneous trachytic breccias — Age of the brown-coal — Peculiar characters 

 of the volcanoes of the upper and lower Eifel — Lake Craters — Trass — Hungarian 

 volcanoes, --------- 665 



Chapter XXXII. — On the different Ages of the Volcanic Hocks, continued. 



Volcanic rocks of the Tertiary period, continued— Extinct volcanoes of Auvergne-^ 

 Mont Dor — Breccias and alluviums of Mont Perrier, with bones of quadrupeds — 

 River dammed up by lava-current — Range of minor cones from Auvergne to the 

 Vivarais — Monts Dome — Puy de Come — Puy de Pariou — Cones not denuded by 

 general flood — Lower Miocene volcanic rocks near Clermont — Hill of Gergovia — 

 Eocene volcanic rocks of Monte Bolca — Trap of Cretaceous periqd — Oolitic pe- 

 riod — New Red Sandstone period — Carboniferous period — " Rock and Spindle" 

 near St. Andrew's — Old Red Sandstone period — Silurian period — Cambrian pe- 

 riod — Laurentian volcanic rocks, ------ 684 



Chapter XXXIII. — Plutonic Bocks — Granite. 



General aspect of granite — Decomposing into spherical masses — Rude columnar 

 structure — Analogy and difference of volcanic and plutonic formations — Minerals 

 in granite, and their arrangement — Graphic and porphyritic granite — Mutual 

 penetration of crystals of quartz and felspar — Occasional minerals — Syenite — 

 Syenitic, talcose, and schorly granites — Eurite — Passage of granite into trap — 

 Examples near Christiania and in Aberdeenshire — Analogy in composition of 



