64 Kansas Academy of Science. 



Dakota contain much salt and gypsum and a bed of lignite. 

 Part of the limestone of the Cretaceous is composed of the 

 shells of rhizopods and is a chalk of the same age as the chalk 

 of England and France. The life of this period is quite 

 modern. Flowering plants, nectar-loving insects, bony fish, 

 reptilian birds and reptilian mammals had been developed 

 from the lower forms of life which preceded them. Among 

 the fossil leaves found in the Cretaceous of Kansas are those 

 of the tulip tree, willow, maple, sassafras, walnut, sequoia and 

 fig. The fruits of the last two have been found well preserved. 

 Reptiles, however, continued to be the dominant type of life. 



At the close of the Cretaceous many of the western moun- 

 tains were rejuvenated and the western half of the continent 

 emerged from the ocean with nearly the present outline, but 

 with much less elevation. Great interior seas occupied the 

 basins throughout the western interior and received the abun- 

 dant sediments from the mountains. 



THE AGE OF MAMMALS. 



The Tertiary period followed the Cretaceous and is noted 

 for the reign of mamnials and the rise of the Rocky Mountains. 

 At first the drainage of Kansas was westward into the interior 

 seas, but later in this period with the rise of the Rocky Moun- 

 tains the slope was reversed and the drainage as we know 

 it to-day became established. The mountains slowly increased 

 their elevation for more than a million years, and the crushed 

 and metamorphosed strata yielded readily to the combined 

 action of the wind, rain and carbonic acid. The high gradient 

 produced by the rise of the Rocky Mountain plateau to an 

 elevation finally exceeding three miles enabled the torrents of 

 rain water which fell at that time to spread coarse and fine 

 debris over the entire plains region as far eastward as central 

 Kansas and Nebraska. The sediments with which western 

 Kansas was flooded at that time consisted of gravel four and 

 five inches in diameter, grading down to fine sand. The peb- 

 bles represented the common rock species of the Rocky Moun- 

 tains. In the list are pebbles of granite, syenite, porphyrj'', 

 rhyolite and basalt, not yet disintegrated, and polished pebbles 

 of quartz. Great lakes occupied the plains of western Kansas 

 and received this debris. As their basins filled, the sediments 

 became on the whole finer and constitute the surface soils in 

 that part of the state. 



