1i HISTOPvY or 



it is otherwise where men and animals have long subsisted : for 

 Hs they make a considerable consumption of wood and plants, 

 both for firing and other uses, they take more from the earth 

 than they return to it ; it follows, therefore, that the bed of ve- 

 getable earth, in an inhabited country, must be always diminish- 

 ing ; and must at length resemble the soil of Arabia Petrea, and 

 other provinces of the East, which having been long inhabited, 

 are now become plains of salt and sand ; the fixed salt always 

 remaining, while the other volatile parts have flown away. " 



If from this external surface we descend deeper, and view the 

 earth cut perpendicularly downwards, either in the banks of 

 great rivers, or steepy sea shores, or going still deeper, if we ob- 

 serve it in quarries or mines, we shall find its layers regularly 

 disposed in their proper order. We must not expect, however, 

 to find them of the same kind or thickness in every place, as 

 they differ in different soils or situations. Sometimes marl is 

 seen to be over sand, and sometimes under it. The most com- 

 mon disposition is, that under the first earth is found gravel or 

 sand, then clay or marl, then chalk or coal, marbles, ores, sands, 

 gravels ; and thus an alteration of these substances, each grow- 

 ing more dense as it sinks deeper. The clay, for instance, 

 found at the depth of a hundred feet, is usually more heavy than 

 that found not far from the surface. In a well which was dug 

 at Amsterdam, to the depth of two hundred and thirty feet, the 

 following substances wer ound in succession :' seven feet of 

 vegetable earth, nine of turf, nine of soft clay, eight of sand, 

 four of earth, ten of clay, four of earth, ten of sand, two of clay, 

 four of white sand, one of soft earth, fourteen of sand, eight of 

 clay mixed with sand, four of sea-sand mixed with shells, then 

 a hundred and two feet of soft clay, and then thirty-one feet 

 of sand. 



In a well dug at Marly, to the depth of a hundred feet, Mr 

 Kuffon gives us a still more exact enumeration of its layers of 

 earth. " Thirteen of a reddish gravel, two of gravel mingled 

 with a ^atrifiable sand, three of mud or slime, two of marl, four 

 of marly stone, five of marl in dust mixed with vitrifiable sand, 

 six of very fine vitrifiable sand, three of earthy marl, three of 

 hard marl, one of gravel, one of eglantine, a stone of the h;i\ii- 



1 Va'PuiuE, as (jiintfJ by Mr Euffon, p. 3.ia 



