Strata Fossiliferoiis. 27 



into the New Eed Marl ; if we pierce the red marl, we 

 reach the water-bearing strata of the New Red Sand- 

 stone. If in certain districts we penetrate the Creta- 

 ceous strata, we are sure to reach the Upper Oolites, 

 and under London many deep wells have been sunk 

 through the Eocene beds, in the certainty of reaching 

 the chalk and finding water. 



It is, therefore, not that the mere surface of the 

 land is formed of various rocks, but the several forma- 

 tions that form the land dip or pass under each other 

 in regular succession, being, in fact, vast beds placed 

 much in the same way as a set of sheets of variously- 

 coloured pasteboard, placed flat on each other, and then 

 slightly tilted up at one end, may slope in one direction, 

 one edge of each sheet being exposed at the surface. 



Vertical sinkings, therefore, in horizontal or slightly 

 inclined strata, often prove practically what we know 

 theoretically, viz. the underground continuity in certain 

 areas of strata one beneath the other. Accurate but 

 more difficult observation and reasoning has done the 

 same for more disturbed strata, so that our island and 

 other countries have been proved to be formed of a series 

 of beds of rock, some many hundreds and some many 

 thousands of feet in thickness, arranged in succession, 

 the lowest stratified formation being of older and the 

 uppermost of younger age. 



Most of these strata are fossiliferous, that is to say 

 they contain shells, bones, and other relics of the crea- 

 tures that lived and died in the waters or water-laid 

 sediments of each special period-, or as sometimes 

 happens, the remains of land plants and terrestrial 

 animals that have been washed into the sea or into 

 lakes. What is the more special evidence on this subject 

 afforded by the rocks ? As we proceed, we shall suppose. 



