THE COMANCHEAN PERIOD 417 



The reptiles had by this time passed their zenith, but the 

 discussion of their decline and the final exit of most of them 

 from the stage of life is reserved for the next Chapter. 



QUESTIONS 



1. Can you suggest from Figure 437 how it may be inferred that 

 the Appalachian Mountains were worn down to a lowland by the 

 Comanchean period ? 





FIG. 437. Generalized section of the Atlantic slope of the United States, 

 showing the relation of the base of the Potomac sediments to the tilted 

 Triassic beds and the folded Paleozoic strata. 



2. Under what conditions might a period of emergence and land 

 conditions not be marked in the section by an unconformity? 

 Where in the United States at the present time are these conditions 

 realized ? 



3. Can you suggest why the Comanchean systtm contains chalk 

 in Texas but marble in central Mexico ? 



4. The Comanchean rocks of California are said to be 25,000 

 feet thick, while in New Jersey they are only 700 feet thick. What 

 reasons may be suggested for this great difference ? 



5. Why are bees now dependent on the angiosperms? 



