CRETACEOUS ERA. 



THE record of this period consists of a series of strata, in 

 which chalk beds make a conspicuous appearance, and which 

 is therefore called the Cretaceous System or formation. In 

 England, a long stripe, extending from Yorkshire to Kent, 

 presents the cretaceous beds upon the surface, generally lying 

 conformably upon the oolite, and in many instances rising 

 into bold escarpments towards the west. The celebrated 

 cliffs of Dover are of this formation. It extends into Northern 

 France, and thence north-westward into Germany, whence it 

 is traced into Scandinavia and Russia. The same system 

 exists in Xorth America, and probably in other parts of the 

 earth not yet geologically investigated. Being a marine 

 deposit, it establishes that seas existed at the time of its 

 formation on the tracts occupied by it, while some of its 

 organic remains prove that, in the neighbourhood of those 

 seas, there were tracts of dry land. 



The cretaceous formation in England presents beds chiefly 

 sandy in the lowest part, chiefly clayey in the middle, and 

 chiefly of chalk in the upper part, the chalk beds being never 

 absent, which some of the lower are in several places. In the 

 vale of the Mississippi, again, the true chalk is wholly, or all 

 but wholly absent. In the south of England, the lower beds 

 are (reckoning from the lowest upwards), 1. Shankland or 

 greensand, " a triple alternation of sands and sandstones with 

 clay ;" 2. Gait, " a stiff blue or black clay, abounding in 

 shells, which frequently possess a pearly lustre ;" 3. Hard 



