J^ - - 



35 



ILLUSTRATIONS OF THE 



gle of 



D 



for a horizontal diftance of 

 is certain, that if thefe ft 



lying one over another, is feen 



h 



miles ; then 

 ive that evtf 



der ground 



pofed, the 

 fared by a 

 tion, is half 



hich may be reafonably fup 



thicknefs of th 



h 



mafs 



mea- 



line perpendicular to its ftratifica^ 

 the horizontal diftance, or amounts 

 . It would alfo require a pit to be 

 funk from the uppermoft of thefe ftrata, to the 

 depth of (2 miles x tan 30°, — ) 6093 feet, be- 



to one mi 



fo 



It 



Id 



fed the undermoft 





and 



therefore, if we fuppofe the fame ftratum to pre- 

 ferve the fame charader for the extent of feme 

 miles, we obtain the fame information from in- 

 fpeaing the edge-feams, and fee in reality as 



far into the bowels of th 



th, as if we had 



funk a perpendicular fhaft to the depth of 60 



fe 



In general, the length of the horizontal hne 



dra 



k^r 



wn acrofs the ftrata, from the loweft in po- 

 iition to the higheft,, multiplied into the fine of 

 the inclination of the ftrata to the horizon, gives 

 the thicknefs of the whole, meafured perpendi- 

 cularly to the plane of the ftratification : and 

 the fame horizontal diftance, multiplied into the 

 tangent of the inclination, gives the adlual depth 

 at which the loweft ftratum would meet a per- 

 pendicularto the horizon, drawn from the high- 

 eft extremity of the upper ftratum. 



In 



