%S NATURAL HISTORY. 



itself has accumulated. The Danube, the Nile, and 

 e!l large rivers, after they have- transported great 

 quantities of slime, sand, &c. never arrive at the sea 

 by a single channel. Marshes are drained everyday; 

 lands, forsaken by the sea, are now ploughed and sown ; 

 we navigate whole countries now covered by the wa- 

 ters. In short, we see so many instances of land 

 changed into water, and water into land, as to con- 

 vince us that, in time, the gulfs of the ocean will be- 

 come continents, the isthmuses will be changed into 

 straits, and the tops of the mountains concerted into 

 shoal y rocks in the sea. 



Still, however, those perpendicular fissures, which 

 are equally diffused through rocks, clays, and every 

 constituent matt rial of the globe, remain to be consider- 

 ed. The perpendicular fissures are indeed placed at 

 greater distances from one another than the horizontal ; 

 and the softer the matter, the more tli.si;ir,t arc the fis- 

 sures. In marble and hard stone, the fissures are only 

 a few feet asunder. If the mass of rock be extensive, 

 the distance between the fissures is some fathoms. 



The cause of perpendicular fissures is easy investi- 

 gated. As various materials constituting the different 

 strata were transported by the waters, and deposited 

 in the form of sediments, they would at first be in a 

 yery diluted state, and would by degrees harden and 

 part with the superfluous quantity of water they con- 

 tained. In the process of drying, they would contract 

 and split at irregular distances. The contraction, 

 therefore, of the parts in drying is the cause of per- 

 pendicular fissures; for I have often remarked, that 

 the sides of tho.se fissures, through their whole e*xtent r 

 correspond as exactly as the two sides of a split piece* 

 of wood. 



