50 



TERRESTRIAL SPHERE. 



most intimately connected with our earthly ex- 

 istence. The description of the heavens, from 

 the far-gleaming nebulous stars (with their 

 suns) down to the central body of our own 

 system, we found limited to such general con- 

 ceptions as volume and quantity of matter. No 

 vital movement is there revealed to our senses. 

 It is only after resemblances, often after fanci- 

 ful combinations, that we arrive at conjectures 

 as to the specific nature of matters of different 

 kinds, as to its [presence or] absence in this 

 or in that planetary body. The heterogeneous- 

 ness of matter, its chemical diversity, and the 

 regular forms into which its particles arrange 

 themselves, as crystals and granules ; its re- 

 lations to the penetrating deflected or decom- 

 pounded waves of light, to radiating, transmit- 

 ted, or polarized heat, to the brilliant, or invis- 

 ible, but not on that account less powerful, 

 phenomena of electro-magnetism — all this vast 

 treasury of physical knowledge, which so ex- 

 alts our views of nature, we owe to the sur- 

 face of the planet we inhabit, and to the solid 

 rather than the fluid element in its constitution. 

 How this knowledge of natural things and nat- 

 ural forces, how the measureless variety of ob- 

 jective perceptions, calls forth the intellectual 

 activity of our kind, and hastens our progress 

 in improvement, has been already observed 

 upon above. These relations as little require 

 farther development in this place, as the en- 

 chainment of the causes of that material force 

 which the control of a portion of the elements 

 has given to particular nations. 



If it was imperative on me to direct atten- 

 tion to the difference which exists betwixt the 

 nature of our telluric knowledge, and our knowl- 

 edge of heavenly space and its contents, so is 

 it also necessary for me to indicate the narrow- 

 ness of the field from which the whole of our 

 knowledge of the heterogeneousness of matter 

 is derived. This field is somewhat inappropri- 

 ately called THE CRUST OF THE EARTH ; it is the 

 thickness of the strata that lie nearest the sur- 

 face of our planet, and that are exposed in deep 

 chasm-like valleys, or by the labour of man in 

 his boring and mining operations. These works 

 scarcely attain a perpendicular depth of more 

 than two thousand feet (less than JLth of a Ger- 

 man mile) below the level of the sea ; conse- 

 quently only ^^^jroth of the semidiameter of the 

 earthC*). The crystalline masses which are 

 ejected by active volcanoes, and which are 

 mostly of the same nature as the rocky matters 

 of the surface, come from unknown, certainly 

 sixty times greater absolute depths than those 

 which the labours -of man have reached. In 

 situations where seams of cozd dip to rise again 

 at distances determinable by accurate measure- 

 ments, it is easy to ascertain the depth of the 

 basin in which the strata lie. In this way we 

 learn, that in some places (Belgium, for exam- 

 ple) the coal measures, together with the or- 

 ganic remains of a former world, which they 

 contain, frequently lie more than five, or ev«n 

 six, thousand feet below the present level of 

 the sea(") : aye, that the mountain limestone 

 and Devonian basin-shaped bent strata, descend 

 even to twice that depth. If we now contrast 

 these subterraneous basins with the mountain 

 summits which have hitherto been held as the 

 highest portions of the uplifted crust of the 



earth, we obtain a distance of 37,000 feet, w 

 nearly ^^th of the earth's semidiameter te- 

 twixt the point of extreme descent and that of 

 highest elevation. This, in the perpendicular 

 dimension and space-filling superposition of 

 rocky strata, would still be the only theatre of 

 geognostic investigation, even did the general 

 surface of the earth reach the height of Dhaw- 

 alagiri, in the Himalaya chain, or of Sorata, in 

 Bolivia, All that lies under the sea level deep- 

 er than the basins referred to above, than the 

 works of man, than the bottom of the ocean, 

 attained in various places with the plumb-line 

 (Sir James Ross sounded with 25,400 feet of 

 line, without reaching the bottom), is even as 

 much unknown to us as is the interior of the 

 other planets belonging to our system. We 

 also know but the mass of the whole earth and 

 its mean density, compared with the superior 

 and to us solely accessible strata. "Where all 

 knowledge of the chemical and mineralogical 

 natural constitution of the interior of the earth 

 fails us, we are again thrown upon conjecture, 

 just as we are with reference to the farthest 

 bodies that revolve about the sun. We can de- 

 termine nothing with certainty upon the depth 

 at which the rocky strata of the crust of the 

 globe should be regarded as existing in a tena- 

 cious softened state, or as a molten liquid ; 

 upon the cavities filled with elastic vapours ; 

 upon the condition of liquids when they are 

 heated red-hot under enormous pressures ; or 

 upon the law of the increment of density from 

 the surface of the earth down to its centre. 



The consideration of the increment of tem- 

 perature of the interior of our planet with in- 

 creasing depths, and of the reaction of the in- 

 terior upon the surface, has led us to the ex- 

 tensive series of volcanic phenomena. These 

 manifest themselves as earthquakes, effusions 

 of gaseous fluids, hot springs, mud-volcanoes, 

 and lava-streams, from craters ; the influence 

 of elastic force is also shown in unquestionable 

 alterations in the level of the general surface. 

 Extensive levels, variously-partitioned conti- 

 nents, are upheaved or sunk ; the solid is part- 

 ed from the fluid ; but the ocean itself, trav- 

 ersed by hot and cold currents that flow through 

 it like rivers, congeals at either pole, and sets 

 into solid rocky masses, here stratified and 

 immoveable, there broken into moveable packs 

 and islets. The boundaries of the sea and 

 land, of the fluid and the solid, are variously 

 and frequently changed. Plains, too, oscillate 

 upwards and downwards. After the elevation 

 of continents, long clefts or chasms took place, 

 mostly parallel to one another, and then, in all 

 probability, at similar epochs in time, and 

 through them, were mountain-chains upheav- 

 ed : salt pools and great inland seas, which 

 were long inhabited by the same creatures, 

 were forcibly separated. The fossil remains 

 of shells and zoophytes bear witness to their 

 original connection. And so we come, follow- 

 ing the relative dependence of phenomena, from 

 the consideration of the fashioning forces, work- 

 ing deep in the interior of the earth, to that 

 which shakes and shatters its upper crust, and 

 which, through the force of elastic vapours, 

 flows out as a molten stream of earth (lava) 

 from open fissures. 



The same forces that uplifted the Andes and 



