402 



MINERALOGY. 



Geognosy, it if thousands, or only some hundreds of centuries had 

 '"""Y"'' elapsed since our continents first existed above the level 

 of the sea, does it not evidently appear that all the 

 country on the west of the Nile would have been bu- 

 ried under this sand before the erection of the cities of 

 ancient Egypt, how remote soever that period may be 

 supposed ; and that, in a country so long afflicted with 

 sterility, no idea would even have been formed of con- 

 structing s uch vast and numerous edifices ? When 

 these cities indeed were built, another cause concurred 

 in favouring their prosperity. The navigation of the 

 Red Sea was not then attended with any danger on the 

 coasts ; all its ports, now nearly blocked up with reefs 

 of coral, had a safe and easy access ; the vessels laden 

 with merchandize and provisions could enter them and 

 depart without risk of being wrecked on these shoals, 

 which have risen since that time, and are still increas- 

 ing in extent. 



" The defects of the present government of Egypt, 

 and the discovery of the passage from Europe to india 

 round the Cape of Good Hope, are therefore not the 

 only causes of the present state of decline of this coun- 

 try. Ifthexantls of the desert had not invaded the 

 bordering lands on the west, if the work of the sea po- 

 lypi in the Red Sea had not rendered dangerous the ac- 

 cess to its coasts and to its ports, and even filled up 

 some of the latter, the population of Egypt and the ad- 

 jacent countries, together with their product, would 

 alone have sufficed to maintain them in a state of pros- 

 perity and abundance. But now, though the passage 

 to India by the Cape of Good Hope should cease to 

 exist, though the political advantages which Egypt en- 

 joyed during the brilliant period of Thebes and Mem- 

 phis should be re-established, she could never again at- 

 tain the same degree of splendour. 



" Thus the reefs of coral which had been raised in 

 the Red Sea on the east of Egypt, and the sands of the 

 desert which invade it on the west, concur in attesting 

 this truth : That our continents are not of a more re- 

 mote antiquity than has been assigned to them by the 

 sacred historian in the book of Genesis, from the great 

 era of the Deluge." 



Chemical Sea-salt affords us examples of the chemical forming 



forming ef- effect of water, as is exemplified in the lakes of the 



fectsof wa- Tauride, in Southern Africa, and many other places. 



ter. We there observe beds of salt formed by precipitation 



from the waters of the lakes ; and sometimes these beds 



alternate with others of clay and loam, and vary much 



in their degree of inclination. Bog iron-ore, which is 



forming daily, is another example of the same kind of 



formation. Morass-ore sometimes alternates in beds 



with peat ; and swamp-ore sometimes occurs in thin 



beds, covering the more compact kinds of peat. Peat 



itself may be ranked as one of the substances formed by 



chemical agency. 



The vast accumulations of calc-sinter found in lime- 

 stone caves, as in those of Derbyshire, the Hartz, the 

 Fichtelgebirge, Antiparos, Gibraltar, &c. belong also to 

 the chemical formations. Calc-sinter is found usually 

 in inclosed spaces, whereas calc-tuff is formed in open 

 spaces. This substance is deposited sometimes in caves, 

 and frequently in fissures, forming veins, which are in 

 this manner filled with very compact calc-sinter, and 

 sometimes even with crystallized calc-spar. Calc-tuff 

 is formed by calcareous brooks emptying themselves 

 into hollows, and thus affording an opportunity for the 

 deposition of their calcareous contents. Near Canstadt 

 in Wurtetnberg, stre-ims of this- kind incrust every thing 

 in their vicinity with calc-tuff, which approaches more 



or less to calc-sinter. If such streams flow into situa- Geognosy, 

 tions where the water has repose and time to deposite ***V*"* 

 its calcareous contents, calcareous beds or strata are 

 formed, which are more or less porous. This porosity 

 is increased on the land, by the tuff mixing with reeds 

 and grass. In beds of this substance skeletons of ex- 

 tinct quadrupeds are met with. 



Destroying and forming effects of Volcanoes. 



The operation of volcanoes is still more limited and 

 local than that of water. Although we are entirely ig- 

 norant of the means employed by nature in producing 

 volcanic fire, we can judge by its effects of the changes 

 it is capable of producing upon the surface of the earth. 

 When a volcano announces itself after some shocks of 

 an earthquake, it forms for itself an opening. Stones 

 and ashes are thrown to a great distance, and lava is 

 vomited forth. The more fluid part of the lava runs in Destroying 

 long streams, while the less fluid portion stops at the an d form- 

 ede of the opening, raises it all round, and forms a ing effects 

 line terminated by a crater. Thus volcanoes accumu- of volca- 

 tate substances on the surface that were formerly bur- noes - 

 ried deep in the bowels of the earth, after having 

 changed or modified their nature or appearances, and 

 raise them into mountains. By these means, they have 

 formerly covered some parts of the continents, and have 

 suddenly produced mountains in the middle of the sea. 

 But these mountains and islands have always been com- 

 posed of lava, and the whole of their materials have 

 undergone the action of fire. Volcanoes have never 

 raised up or overturned the strata, through which their 

 apertures pass, and have in no degree contributed to 

 the elevation of the great mountains which are not vol- 

 canic *. 



CHAP. III. 



INTERNAL STRUCTURE OF THE EARTH. 



Having in the preceding Chapters described the va- 

 rious inequalities observable on the earth's surface, and 

 stated the means which nature appears to have employ- 

 ed in forming them, we come now to the consideration 

 of the second branch of Geognosy, which makes us ac- 

 quainted with the internal structure of the earth. 



At first sight the solid mass of the earth appears to 

 be a confused assemblage of rocky masses piled on each 

 other without order or regularity : tothesuperficial obser- 

 ver, nature appears, in the apparently rude matter of the sl " rl ^ t n ure 

 inorganic kingdom, to present us as only with a picture of tne 

 of chaos, where none of those admirable displays of skill earth, 

 and contrivance, which, in the structure of animals and 

 vegetables so powerfully excite our attention, and claim 

 our admiration, are to be observed. It is not surpri- 

 sing that this unfavourable opinion should have long 

 continued to be prevalent, when we consider the expe- 

 rience, skill, and judgment which are necessary for 

 enabling us to unravel all the variety of apparently un- 

 connected relations, which are observable in the inter- 

 nal structure of the earth. In ancient writers we find 

 nothing on this important subject ; and it is only by 

 the light of modern discoveries, that we have been en- 

 abled to trace out those beautiful arrangements that 

 prevail in the mineral kingdom. Of these, we shall 

 now give a concise and accurate description, and at 

 same time state some of those inferences that appear to 

 be deducible from these various relations and appear- 

 ances. But these descriptions and inferences can only 

 be fully understood, and the gratification derived from 



Cuvier'e Theory of the Earth. 



