THE CllUST OP THE EARTH. 



Wenlock formation ..... 1 800 feet 

 Lucllow formation . ... 2000 



Old red sandstone ..... 1000 

 Carboniferous or mountain limestone i 500 to 2500 

 Millstone grit . . . . 500 to 700 

 Coal formation . . . . . 3000 



Lower new red Pontefract rock . . 100 



Magnesian limestone . . . 300 



New red sandstone 1000 



Lias ........ 1000 



Lower or Bath oolite . . . 400 to goo 

 Middle or coralliue oolite . . 300 to 800 



Upper or Portland oolite . . 200 to 800 



Green sand formation . . . . 



Chalk formation 



Lower tertiary or eocene, about . . . 1200 ,, 



Miocene formation. 



Pleiocene. 



Pleistocene. 



Rough as this approximation is, it may give some idea of the 

 general thickness, at least, of the stratified part of the crust of 

 the earth. It would appear from combining these results, that 

 the total thickness of the stratified crust, as far as these 

 observations go, varies from 10 to 20 miles. Of this thickness 

 the lower, or palaeozoic strata, constitute the principal part, as 

 will be seen by the annexed diagram given by Professor Phillips. 



Tertiary or Upper Strata. 



Secondary or Middle Strata. 



Primary or Lower Strata. 



52 



