[vi] COSMOS. 



internal planetary activity. There rise from the depths of the earth 

 through fissures and cones of eruption, various gases, liquid fluids (pure 

 or acidulated), mud and molten earths. Volcanoes are a species of 

 intermittent spring. Temperature of thermal springs ; their constancy 

 and change. Depth of the foci (pp. 218-221 and notes). Salses, 

 mud-volcanoes. Whilst fire-emitting mountains being sources of molten 

 earths, produce volcanic rocks, spring water forms, by precipitation, 

 strata of limestone. Continued generation of sedimentary rocks (p. 

 226 and note). 



d. Diversity of volcanic elevations. Dome-like closed trachytic 

 3iiountains. Actual volcanoes which are formed from craters of eleva- 

 tion or among the detritus of their original structure. Permanent con- 

 nection of the interior of our earth with the atmosphere. Kelation to 

 certain rocks. Influence of the relations of height on the frequency 

 of the eruptions. Height of the cone of cinders. Characteristics of 

 those volcanoes which rise above the snow-line. Columns of ashes and 

 fire. Volcanic storm during the eruption. Mineral composition of 

 lavas (p. 234 and notes). Distribution of volcanoes on the earth's 

 surface; central and linear volcanoes; insular and littoral volcanoes. 

 Distance of volcanoes from the sea-coast. Extinction of volcanic forces 

 (p. 245 and notes). 



e. Relation of volcanoes to the character of rocks. Volcanic /orces 

 form new rocks, and metamorphose the more ancient ones. The study 

 of these relations leads by a double course to the mineral portion of 

 geognosy, (the study of the textures and of the position of the earth's 

 strata), and to the configuration of continents and insular groups ele- 

 vated above the level of the sea (the study of the geographical form 

 and outlines of the different parts of the earth.) Classification of rocks 

 according to the scale of the phenomena of structure and metamorphosis, 

 which are still passing before our eyes. Rocks of eruption, sedimentary 

 rocks, changed (metamorphosed) rocks, conglomerates compound rocks 

 are definite associations of oryctognostically simple fossils. There are 

 four phases in the formative condition ; rocks of eruption, endogenous 

 (granite, sienite, porphyry, greenstone, hypersthene, rock, euphotide, me- 

 laphyre, basalt, and phonolithe) ; sedimentary rocks (silurian schist, coal 

 measures, lime stone, travertine, infusorial deposit); metamorphosed 

 rock, which contains also together with the detritus of the rocks of 

 eruption and sedimentary rocks, the remains of gneiss, mica schist, and 

 more ancient metamorphic masses. Aggregate and sandstone forma- 

 tions. The phenomenon of contact explained by the artificial imita- 

 tion of minerals. Effects of pressure and the various rapidity of 

 cooling. Origin of granular or saccharoidal marble, silicification of 

 schist into ribbon jasper. Metamorphosis of calcareous marl into 

 micaceous schist through granite. Conversion of dolomite and gra- 

 nite into argillaceous schist, by contact with basaltic and doleritie 

 rocks. Filling up of the veins from below. Processes of cemen- 

 tation in agglomerate structures. Friction conglomerates (p. 271 

 and note). Relative age of rocks, chronometry of the earth's crust 

 Fossiliferous strata. Relative age of organisms. Simplicity of the first 



