tlfitATING to THE FIGURE OF THE EARTH. jfjl 



'20. In the part of England, where the meafures we are now Obfervations to 

 treating of have been taken, theftrataare of chalky and though irregularity pro'- 

 of great extent, are bordered, on all the fides that we halve bablyarlfes from 

 accefs to examine^ by ftrata much denfer and more compad. ft^ncesT""*" 

 Toward the weft the chalk is fucceeded by limeftone, ftnd that 

 limeftone by the primitive fchiftus and granite of the weft of 

 Devonlhire and of Cornwall. On the eaft we may fuppofe 

 that fomething of the fame kind takes place, though the fea 

 prevents us from obfervihg it, as the chalky and argillaceous 

 beds extend in this diredtion to the coaft, and probably to 

 fome diftance beyond it. Now the meridian of Greenvvich The merldlaa of 

 may be confidered as dividing the trad of country, occupied ^''*^^"^'^'? ?P* 



J » ^ J ' t pears to divide a 



by thefe lighter ftrata, into two parts, in fuch a manner, that- chalk country, 

 the plummet being carried to a diftance from it, either eaft or ^^f ■"& on each 

 welt, approaches to the denier ftrata, and is ot courle attracted ib-ata of lime- 

 by them, fo that the zenith is forced back, as it were, to the ^""^j fchiftus, 

 meridian of Greenwich, and does not recede from it, in the which^Ty^at- 

 heavens, at fo great a rate as the plummet itfelf does, on trading the 

 the earth. Hence the longitudes from this meridian, eftimated li^^^ wav^out- 

 by the arches in the heavens, intercepted between the zenith wards, muft re- 

 and the faid meridian, will appear lefs than they ought to do ; ^j"^^ * longer 

 and too much fpace on the furface of the earth will of confe- ingorwefting to 

 quence be afljgned as the meafure of a degree. In this way correfpond with 

 D' is made too great ; and we may fuppofe the circurhftances igftjai arc. 

 fuch that D, on going north or fouth, h not enlarged in the 



jy D . 



fame proportion; hence ■ will be augmented, and of 



(^ 

 courfe - will be reprefented as too great. This explanation 

 a 



may perhaps appear very hypothetical, and it is certainly pro- 



pofed merely as a hypothefis. It is a hypothefis, too, that 



lays claim only to a temporary indulgence, as it is propofed 



at the very moment when it may be brought to the trial, and 



when, by a further continuation of the furvey toward the-jiorth, 



it will probably be determined how far the diftribution of the 



ftrata of this country affeds the direflion of gravity. It will 



indeed be curious to remark what irregularities take place on 



advancing into the denfer ftrata of the north. The limeftone. 



and fandftone ftrata of the middle part of the iftand will fucceed^ 



to the chalk of the fouth, the primitive and denfer ftrata ftill ' 



I 2 occupying 



