THE MESOZOrC AGES. 



229 



crumpling-up of the Appalachians and the Urals, and 

 the older hills of Western Europe. The Cretaceous 

 collapse led to the crumpling of the great N.W. and 

 S.E. chain of the Rocky Mountains and Andes, and 

 to that of the east and west chains of the south of 

 Asia and Europe. The cause was probably in both 

 cases the same ; but the crust gave way in a different 

 part, and owing to this there was a greater amount 

 of submergence of our familiar continental plateaus 

 in the Cretaceous than in the Permian. 



Another remarkable indication of the nature of the 

 Cretaceous subsidence, is the occurrence of beds filled 

 with grains of the mineral Glauconite or ''green- 

 sand.'' These grains are not properly sand, but little 

 concretions, which form in the bottom of the deep sea, 

 often filling and taking casts of the interior and fine 

 tubes of Foraminiferal shells. Now this Glauconite, 

 a hydrous silicate of iron and potash, is akin to similar 

 materials found filling the pores of fossils in Silurian 

 beds. It is also akin to the Serpentine filling the 

 pores of Eozoon in the Laurentian. Such materials 

 are formed only in the deeper parts of the ocean, 

 and apparently most abundantly where currents of 

 warm water are flowing at the surface, as in the area 

 of the Gulf Stream. Thus, not only in the prevalence 

 of Foraminifera, but in the formation of hydrous sili- 

 cates, does the Cretaceous recall the Laurentian. Such 

 materials had no doubt been forming, and such animals 

 living in the ocean depths, all through the intervening 

 ages, but with the exception of a few and merely 



