396 



GEOLOGY. 



on the surface of tlie land, in lakes, rivers, on 

 roasts, or on the bottom of the sea. During land 

 fl.x.nis, the water does not always convey its mechani- 

 cally mixed parts to rivers ; on the contrary it often 

 deposites them in hollow places. Those particles that 

 reach rivers, form sand-banks, particularly in slow- 

 flowing rivers. Very extensive mechanical formations 

 iire daily taking- place on the coasts, and even in some 

 places at a considerable distance from them, by the 

 Caters of the ocean. In the Baltic or East sea, 

 many appearances of this kind are to be observed. 

 Thus the bay of Fulbaka, which was navigated with 

 boats within the memory of man, is now filled up and 

 covered with grass. Several harbours in Lapland 

 that formerly admitted vessels, are now three or four 

 thousand paces from the sea ; and at Helsingor there 

 are iron works in places which were covered by the 

 sea about eighty years ago. The whole of the 

 ancient kingdom of Prussia appears to have been 

 formed in this manner ; it is said that the sea reached 

 as far as Culm within the period of human history. 

 The city of Dantzic, several hundred years ago, was 

 close on the sea-shore. 



Similar appearances occur on other coasts. Be- 

 tween the coasts of Norfolk and Zealand in Holland, 

 there is a great sand-bank where opposite currents 

 meet, and it is probable that this bank will in time 

 form an island, and probably even an isthmus. Much 

 of the country of the United Provinces has been pro- 

 duced by the forming action of the sea. 



A great portion of the flat country from the mouth 

 of the Rhone to the Pyrenees, is said to be the work 

 of the ocean ; and the whole tract of country 

 from Pisa to Leghorn, is a formation of the same 

 nature. 



In those parts of the sea where its waters are but 

 little agitated, similar forming effects are to be ob- 

 served. 



Where marine currents flow rapidly, and near the 

 coast, they exert a destroying power, but when they 

 act at a distance, a forming power. 



The effects produced by the sea alone, without the 

 aid of rivers, are far less beneficial. When the sea- 

 coast is low, and the bottom consists of sand, the waves 

 push this sand towards the shore, where, at every 

 reflux of the tide, it becomes partially dried ; and 

 the winds, which almost always blow from the sea, 

 drift up some portion of it upon the beach. By 

 this means downs, or ranges of low sand-hills are 

 formed along the coast. These, if not fixed by the 

 growth of suitable plants, either sown by nature, or 

 planted by human industry, would be gradually, 

 but certainly carried towards the interior, covering 

 up the fertile plains with their sterile particles, and 

 rendering them unfit for the habitation of mankind, 

 because the same winds which carried the loose dry 

 sand from the shore to form the downs, would neces- 

 sarily continue to drift that which is at the summit 

 further towards the land. On the east coast of Scot- 

 land, and in many of the islands, there are striking 

 effects of this kind. The sands of the Lybian desert 

 have left no lands capable of tillage on any part of 

 the western luniks of the Nile not sheltered by 

 mountains. Summits of the ruins of ancient cities 

 buried by these sands still appear externally. 



Sea-salt affords us examples of the chemical form- 

 ing effect of water, as is exemplified in the lakes of 

 the Tauride, in Southern Africa, and many other 

 places. 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 inclina- 

 tion. 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 

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

 the Fichtelgebirge, Antiparos, Gibraltar, &e., belong 

 also to the chemical formations. Calc-sinter is found 

 usually in enclosed spaces, whereas calc-tuff is formed 

 in open spaces. This substance is deposited some- 

 times in caves, and frequently in fissures, forming 

 veins, which are in this manner filled with very com- 

 pact 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 Wirtemberg, streams of 

 this kind incrust every thing in their vicinity with 

 caic-tuff, which approaches more or less to calc-sinter. 

 If such streams flow into situations where the water 

 has repose and time to deposite 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 extinct quadru- 

 peds are met with. 



Destroying and forming effects of fire. Although 

 we are entirely ignorant 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 long streams, while the less 

 fluid portion stops at the edge of the opening, raises 

 it all round, and forms a line terminated by a crater. 

 Thus volcanoes accumulate substances on the surface 

 that were formerly buried 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 moun- 

 tains in the middle of the sea. 



The changes which earthquakes produce on the 

 earth's surface form an important consideration in 

 geology. Werner distinguishes two kinds of earth- 

 quakes. Some, he says, appear to be connected with 

 a particular volcano, and to have their focus in the 

 same region as it. They are only felt to the distance 

 of a few leagues around, and their paroxysms are 

 almost always connected with those of the volcano. 

 Others, which appear to have their foous at a much 

 greater depth, and whose effects are much greater, 

 are propagated to immense distances with incredible 

 celerity, and are felt almost at the same time al 

 points thousands of miles distant from each other. 

 Some of the latter, however, approach the former, 

 and are still connected with volcanic phenomena. 

 Thus, during the earthquake which overturned Lima 

 in the year 1746, and which was one of the most 

 terrible that has been recorded, four volcanoes 

 opened in one night, and the agitation of the earth 

 ceased. 



If in the more violent we include the slighter agi- 

 tations of the earth's surface in particular places, 

 earthquakes may be said to be universal or general, 

 and we may affirm that no considerable country is 

 entirely exempted from them. Sandy deserts and 

 fertile regions, primitive, secondary, and tertiary 

 hills, extensive plains, and even marshy districts but 

 little elevated above the level of the sea, afford no 

 protection against these destructive phenomena, 

 which are equally prevalent in cold, in temperate, 

 and in tropical climates. They are, however, gene- 



