Chap. 45-1 Inequalities of Earth* s Surf ace. 2*9 



towards the weft, and- have a more gentle, .declivity 

 towards the eaft ; hence the weflern coatl of countries 

 is almoft always deeper than the eaftern. The back 

 of a mountain fhe\vs the obliquity with which the 

 ftrata fmk into the ground ; the abrupt edge of the 

 flrata becomes more/ Hoping, as time, producing a 

 gradual decay, draws the rubbifh from above. Where 

 the face of a country is fo irregular, its appearance 

 depends on the different hardnefs or foftnefs of the 

 flrata. The abrupt rocks, which we obferve in many- 

 parts, feem to have been composed of an adventitious 

 mixture of different ftrata, which have refifted the in- 

 juries of time with unequal force. 



Between the ftrata, layers of different clays are in- 

 terpofed, which are called by the miners way-boards j 

 they are feldom more than four or five, and in fome 

 inftances not more than one foot thick ; they ferve 

 to mark and diftinguiih the different ftrata, for in fact 

 the ftrata are themfelves compofed of different la- 



Every part of a ftratum may be coftfidered as equally 

 thick when covered with an incumbent bed; but 

 when expofed to the action of the air, and other exter- 

 nal agents, a. great part of it, whether grit, lime-ftone, 

 or toad-flone, .is decompofed and converted into earth. 

 or mould. Immediately under the foil the fragments 

 of ftone are fmall, and gradually increafe to the depth 

 of fifteen or twenty feet, where it commonly appears 

 folid, and fit for the mafon. Strata are ufually inter- 

 rupted by clefts or fiffures at different diftances, which 

 feem to have been the effects of violence. In thefe 

 fifiures only the ores of metals are to be found. 



It has been remarked, that we cannot, by digging 

 into the earth, obtain a view of the pofition and nature 



Whitehurft, Chap. XVI. 



VOL, II. U of 



