248 BERTHA'S VISIT TO HER 



torrents, we can perceive somewhat of its in- 

 terior structure thus laid open to us. 



The low and level parts of the earth, when 

 penetrated to a great depth, generally exhibit 

 parallel strata, composed of various substances, 

 and most of them containing vegetable and 

 animal, and innumerable marine productions. 

 Similar strata, with the same kind of productions, 

 compose the hills even to a great height ; and some- 

 times the shells are so numerous, that an entire 

 stratum seems to be formed of them. These 

 shells are frequently in such perfect preservation, 

 that they retain their sharpest ridges, and their 

 tenderest forms. They are sometimes found 

 incrusted in hard stone, and sometimes inclosed 

 in loose sand or clay \ and the nicest comparison 

 cannot detect any difference between the texture 

 of these shells, and those which now inhabit the 

 sea. It is, therefore, fair to conclude, that they 

 also must have formerly lived in the sea, and, 

 consequently, that the sea must once have flowed 

 over those places. 



But we must not forget that in some countries 

 none of these remains occur, for instance, in 

 Cornwall, airl the highlands of Scotland ; while 

 in others, not a well can be sunk, or a pit opened, 

 without presenting them in abundance ; as in the 

 south-eastern counties of England. The reason of 

 this difference will, I am sure, have suggested 

 itself, if you recollect our former conversation's : 



