CHAPTER XVI 

 THE CRETACEOUS PERIOD 



Origin of Name, Subdivisions, etc. 



The term Cretaceous, from the Latin "Creta" for chalk, was 

 given to the period because of the prominence of chalk beds in 

 the rocks of this age, especially in England and France. In fact, 

 one of the most striking features of the landscape in southern 

 England and northern France consists in the frequent exposures 

 of beds of white or very light colored chalk. Perhaps the most 

 famous are the Dover Cliffs of England. In many parts of the 

 world, however, the Cretaceous system is not rich in chalk deposits. 

 In the United States, chalk is extensively developed in the Creta- 

 ceous of Alabama and Texas. The system was first carefully 

 studied in England, but the names of the French subdivisions are 

 now more widely employed. 



For a long time the Cretaceous system has been known to be 

 divisible into two portions — a Lower and an Upper — often 

 separable by unconformity, and, during the past ten or twelve 

 years, some authors have regarded the Lower Cretaceous as a 

 separate system called "Comanchean" from a locality in Texas. 

 Recent work has, however, shown that the Lower and Upper 

 Cretaceous are not so sharply and widely separated as was formerly 

 supposed, particularly in the type region of Texas. Hence the use 

 of "Comanchean" as a distinct system and period name seems 

 inadvisable at the present time. 



Following are the principal subdivisions of the Cretaceous 

 as now recognized in Europe and North America, though exact 

 correlations are not implied (see page 237). 



Distribution and Character of the Rocks 



General Distribution. — Lower Cretaceous. The surface dis- 

 tribution of rocks of known Lower Cretaceous age is shown on 

 the accompanying map (Fig. 148). With the exception of part of 



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