BREAKS IN THE SUCCESSION 295 



its progress was rapid. One of the most important 

 lessons it learnt was that if we want to know how the 

 world was made, the first essential is to study the 

 earth itself, to investigate with patient drudgery every 

 detail it presents, and particularly the structures that 

 can be seen in river-banks, sea-cliffs, quarries, pits, 

 and mines. Thus it discovered that the solid land 

 beneath our feet is to a large extent composed of layers 

 of sediment which were once deposited more or less 

 quietly at the bottom of ancient seas, and certain curious 

 bodies known as fossils, it concluded to be the remains 

 of plants and animals, sea-shells, and the like, which 

 were once the living denizens of these seas. 



It discovered that these deposits lie so regularly one 

 upon another, that it compared them to a pile of books, 

 or to a slanting row of books lying cover to cover ; 

 and that in some cases at least the simile was not 

 strained, will appear if we trace the structure of England 

 from Oxford westwards towards Bristol. We then find 

 that the thick bed of clay upon which Oxford stands 

 lies evenly on a series of gently-sloping beds known 

 as the lower Oolites ; these in like manner repose on 

 those thin seams of limestone and clay called the Lias, 

 and these in their turn upon the red beds of the Trias. 

 It might, perhaps, have been expected that this uniform 

 arrangement would continue through the whole thickness 

 of the stratified rocks, but it was discovered, and the 

 importance of the discovery was recognised so early as 

 1670 by Bishop Steno, a man of great genius, that 

 the regularity of the succession is liable to interruption at 

 intervals. Thus as we approach Bristol we encounter 

 those beds of limestone which are associated with our 

 coal-bearing strata, and which are consequently called 

 "Carboniferous"; but these are by no means related 

 to the beds we have just passed over in the same manner 



