THE EARTH. 53 



rifiable sand, three of slime, two of marl, four 

 of marly stone, five of marl in dust mixed with 

 verifiable 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 hard- 

 ness 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 vit- 

 rifiable sand mixed with fossil-shells, two of fine 

 gravel, three of stony marl, one of coarse powder- 

 ed marl, one of stone calcinable like marble, three 

 of grey sand, two of white sand, one of red sand 

 streaked with white, eight of grey sand with 

 shells, three of very fine sand, three of grit, 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 adduc- 

 ed instances, we might have observed, that the 

 last layer was fifteen feet thick, while most of the 

 others were not above eight ; and this might have 

 gone much deeper, for aught we can tell, as, 

 before they got through it, the workmen ceased 

 digging. 



These layers are sometimes 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, 



