540 



THE CRETACEOUS PERIOD 



Pacific coast by the marine Chico series. At the time of its origin, 

 this series probably extended along the coast from Lower California 

 to the Yukon. The Chico series rests on the Shastan unconformably 

 in some places, and overlaps it at others. The fauna of the Chico 

 series is littoral. Its oldest portion is older than the fauna of the 

 Colorado series, and its youngest is older than the fauna of the 

 youngest Cretaceous beds. 



Close of the Period 



About the close of the Cretaceous period a series of disturbances 

 was inaugurated on a scale which had not been equaled since the 

 close of the Paleozoic era. These changes furnish the basis for the 

 classification which makes the close of this period the close of an era. 

 These disturbances continued into later times, but the close of the 

 Cretaceous may be said to have been the time when the changes 

 had advanced so far as to make themselves felt profoundly. They 

 consisted of deformative movements, a part of which were erogenic, 

 and of igneous eruptions on an almost unprecedented scale. 



General movements. In the closing stages of the period, the 

 sea which had lapped over the Coastal Plains of the Atlantic and 



Km 

 m ? L^?f 



\ 



Fig. 455. Section showing the position of the Cretaceous beds in western 

 Oregon. Mg, meta-gabbro ot unknown age; sp, serpentine; as, amphibolite schist; 

 Jr, Jurassic (?); Km and -Kmw, Cretaceous; Eu, Eocene; Ed, Eocene diabase. 

 (Diller, Roseburg, Ore., folio, U. S. Geol. Surv.) 



Fig. 456. Section showing position of Cretaceous beds at one point in the 

 vicinity of Livingston, Montana. J? = Archean; -, Cambrian; D, Devonian; C, 

 Carboniferous; J, Jurassic; Kd, Dakota formation; Kc, Colorado series; Km, Mon- 

 tana series, and Kl, Laramie series; bbr, basic igneous rock, and apt, acidic rock. 

 Length of section about n miles. (Livingston, Mont., folio, U. S. Geol. Surv.) 



the Gulf of Mexico was withdrawn toward the abysmal basin. At 

 about the same time, the Appalachian Mountains, which had been 

 reduced to a peneplain by this time, were bowed up again. 



It is probable that most of the Cordilleran region was elevated 



