350 



HISTORICAL GEOLOGY. 



continent. The place of the Wahsatch Eange was then 

 the western marginal bottom of this interior sea. 4. The 

 Pacific shore-line was then east of the Coast Kanges, and 

 its waves beat against the lowest foot-hills of the Sierra. 

 This is shown in the map, Fig. 303. 



Character of the Bocks. In regard to the kind of 

 strata, there are two points worthy of passing mention. 



1. Chalk. The period takes its name from the chalk 

 of England and France, which belongs here. Chalk is 

 a soft, snow-white, very pure lime-carbonate, scattered 



FIG. 304. View of Iowa chalk under the microscope. (After Calvin.) 



through which are nodules of flint. On account of its 

 softness, it is worn into strange, castellated forms. Pure 

 chalk, as described, was until recently, supposed to be 

 confined to England, and France, and middle Europe, but 

 has now been found in the Cretaceous of Texas and the 

 Plains. When examined with the microscope, it seems 



