Principal Divisions of Geologic Time." 



a The geologic record consists mainly of sedimentary beds— beds deposited in water. Over large areas 

 long periods of uplift and erosion intervened between periods of deposition. Every such interruption in 

 deposition in any area produces there what geologists term an unconformity. Many of the time divisions 

 shown above are separated by such unconformities— that is, the dividing lines in the table represent local 

 or widespread uplifts or depressions of the earth's surface. 



I> Epoch names omitted; in less common use than those given. 



