16 



CHAP. III. 



On the general Form and Constitution of the Globe. 



THERE are many points in the history of our globe, 

 respecting which Geology and Astronomy mutually 

 throw light on each other. If the variations of gravity 

 on different parts of the surface, and the peculiarities 

 of figure on which they in some measure depend, are 

 subjects for the especial consideration of the Astro- 

 nomer, it is the duty of Geology to investigate those 

 circumstances in the history and condition of the 

 earth with which they are connected. 



Although, in a popular and general sense, the form 

 of the earth is that of a globe, it has long since been 

 established, by the measurement of degrees on diffe- 

 rent parts of its surface, that its figure is not spherical. 

 These trials having shown that the meridional degrees 

 increased in length from the equator towards the 

 poles, it followed that the radius of curvature was less, 

 or shorter, near the former than the latter, or that the 

 earth formed an oblate spheroid, of which the polar 

 axis was less than the equatorial. 



Thus, that which had been previously suspected 

 from mathematical considerations, became apparently 

 proved by mathematical experiments ; namely, that 

 the form of the earth tended, at least, to that which 

 would result from its fluidity at some period of its 

 existence, combined with the rotatory motion of all 

 its parts on the polar axis. 



For this important fact, geology is indebted to 



