166 
IOWA ACADEMY OF SCIENCE 
The channel of the Rio Mora has been pushed to one side of its former 
course by the lava having filled the old canyon and a new canyon has 
been formed in the massive Cretaceous sandstone of the neighborhood. 
This diversion of the river is in many places very marke.d. 
The amount of erosion which has taken place is admirably shown in a 
number of places. The present canyon of the Mora river is in places 
over 1,000 feet deep. The bottom of the old canyon at the time of the 
fiow of laVa was at level abont 250 feet higher than the bottom of the 
channel today. The basalt-stream is about 400 feet in thickness. Above 
its upper surface it is still 500 feet more to the edge of the plan forming 
the general surface of the country. Since the time the lava flowed the 
Rio Mora has been not only forced to corrade an entirely new channel, 
but it has eroded its neiv canyon 250 feet deeper than its old one. 
