OUTLINES OF GEOLOGY. 



69 



was common to two great geological formations, or which 

 existed at the present day. 



158. From these considerations, the inference is certain 

 that the several formations, from the slates upwards, have 

 been deposited in succession, beginning with the inferior 

 order, the epoch of whose deposit is most remote ; that, when 

 two formations are found identical in their organic remains, 

 however remote from each other on the surface of the earth, 

 they belong to the same epoch of the earth's geological his- 

 tory ; and that, where formations are wanting in any 

 place, it is because it was beyond the reach of causes then 

 in action on other parts of the globe, or because they may 

 have been since removed by some geological cause. 



159. It is therefore obvious, that the thickness of the 

 several formations wnich we have described, will be an im- 

 portant element in the investigations to which the third divi- 

 sion of our subject is devoted. These thicknesses, as given 

 by the most recent authorities, are as follows : 



FEET. 



80 



i loo 



Superior order. 



Supermedial order. -I 



Pliocene, 

 Miocene, 



Eocene, 



600 



780 



Medial order. 



Submedial order. 



Chalk, 700 



Green Sand, . 500 



Iron Sand, 950 



Upper Ooolite, 770 



Middle Ooolite, 880 



Lower Ooolite, 820 



LTriasic, . . . • 2100 



f Mill-stone grit, 700 



J Coal measures, f 1000 



J Carboniferous limestone, .... 850 



Do. sandstone and grauwack£, . 10,000 



7720 



Transition limestone, 1800 



Do. slate, 2500 



12,550 



4300 



24,350 



