TIME AND CHANGE 



tent, have gone down and have not yet come up, if 

 they ever will. The great Mississippi Valley was 

 under water and above water time after time during 

 the Palaeozoic period. The last great invasion of 

 the land by the sea, and probably the greatest of all, 

 seems to have been in Cretaceous times, at the end 

 of the Mesozoic period. There were many minor in- 

 vasions during Tertiary times, but none on so large 

 a scale as this Cretaceous invasion. At this time a 

 large part of North and South America, and of Eu- 

 rope, and parts of Asia and Australia went under 

 the ocean. It was as if the earth had exhaled her 

 breath and let her abdomen fall. The sea united the 

 Gulf of Mexico with the Arctic Ocean, and covered 

 the Prairie and the Gulf States and came up over 

 New Jersey to the foot of the Archaean Highlands. 

 This great marine inundation probably took place 

 several million years ago. It was this visitation of 

 the sea that added the vast chalk beds to England 

 and France. In parts of this country limestone beds 

 five or six thousand feet thick were laid down, as well 

 as extensive chalk beds. The earth seems to have 

 taken another hitch in her girdle during this era. 

 As the land went down, the mountains came up. 

 Most of the great Western mountain-chains were 

 formed during this movement, and the mountains of 

 Mexico were pushed up. The Alps were still under 

 the sea, but the Sierra and the AUeghanies were 

 again lifted. 



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