SO A HISTORY OF 



sand mixed with shells, then a hundred and two feet of soft clay, and 

 chen thirty-one feet of sand. 



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

 gives us a still more exact enumeration of its layers of earth. " Thirteen 

 of a reddish gravel, two of gravel mingled with a vitrifiable 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 hardness and grain of marble, one of gravelly marl, one 

 of stony marl, one of a coarser kind of stony marl, two of a coarser 

 kind still, one of vitrifiable sand mixed with fossil-shells, two of fine 

 gravel, three of stony marl, one of coarse powdered marl, one of stone, 

 calcinable like marble, three of gray sand, two of white sand, one of red 

 sand streaked with white, eight of gray sand with shells, three of very 

 fine sand, three of a hard gray stone, four of red sand streaked with 

 white, three of white sand, and fifteen of reddish vitrifiable sand." 



In this manner the earth is every where found in beds over beds ; and, 

 what is still remarkable, each of them, as far as it extends, always main- 

 tains exactly the same thickness. It is found also, that as we proceed 

 to considerable depths, every layer grows thicker. Thus in the ad- 

 duced instances we might have observed, that the last layer was fif- 

 teen feet thick, while most of the others were not above eight, and 

 this might have gone much deeper, for ought we can tell, as before 

 they got through it the workmen ceased digging. 



These layers are sometimes very extensive, and often are found to 

 spread over a space of some leagues in circumference. But it must 

 not be supposed that they are uniformly continued over the whole 

 globe without any interruption : on the contrary, they are ever, at 

 small intervals, cracked through as it were by perpendicular fissures ; 

 the earth resembling, in this respect, the muddy bottom of a pond, 

 from whence the water has been dried off by the sun, and thus gaping 

 in several chinks, which descend in a direction perpendicular to its 

 surface. These fissures are many times found empty, but oftener* 

 closed up with adventitious substances, that the rain, or some 

 other accidental causes, have conveyed to fill their cavities. Their 

 openings are not less different than their contents, some being not 

 above half an inch wide, some a foot, and some several hund-ed yards 

 asunder. These last form those dreadful chasms that are to be found 

 in the Alps, at the edge of which the traveller stands dreading to look 

 down at the immeasurable gulf below. These amazing clefts are well 

 known to such as have passed these mountains, where a chasm fre- 

 quently presents itself several hundred feet deep, and as many over, 

 at the edge of which the way lies. It often happens also, that the 

 road leads along the bottom, and then the spectator observes on each 

 side frightful precipices several hundred yards above him ; the sides 

 of which correspond so exactly with each other, that they evidently 

 seem torn asunder. 



But these chasms, to be found in the Alps, are nothing to what 

 Ovalle tells us are to be seen in the Andes. These amazing moun- 

 tains, in comparison of which the former are but little hills, have their 

 fissures in proportion to their greatness. In some places they are 9 



