IOWA CAMBRIC SUCCESSION 
313 
TERRANAL DIFFERENTIATION OF IOWA CAMBRIC 
SUCCESSION^ 
By Charlks Keyes. 
Partly because of the fact that there is apparently such paucity 
of organic remains contained in them, and partly owing to the 
circumstance that they occupy so restricted an area within the 
limits of our state the formations of Cambric age receive scant 
treatment and discription with little detail. Despite their nar¬ 
rowly exposed extent these rocks really constitute one of the 
great geological successions of our commonwealth. Notwith¬ 
standing their threadlike outcrop in the vertical cliffs of the 
Mississippi gorge they are yet known, through means of deep- 
well records, corroborated by sky observations north and east, 
in Wisconsin and Minnesota, to have a maximum thickness of 
upwards of 1000 feet. 
Although, curiously enough, these rocks were among the first 
within the limits of our state to get modern scientific considera¬ 
tion they remain, today, hardly better understood than when 
Owen, three-quarters of a century ago, retired from the field. 
Even the late'Governmental and State surveys seem to add little 
that is new or definite to our very antiquated knowledge. 
In reality, so limited are Cambric rock outcrops within our 
boundaries that some of the terranes cannot be adequately, or 
properly treated by themselves. They have to be regarded in 
connection with the same formations of nearby states. Geological 
science knows no political boundaries. Discussion of the larger, 
or continental, relationships of these rocks is for the first time 
possible. 
With something of their broader aspects in mind, I recently 
had opportunity to study rather closely that magnificent section 
1 Paper read before the Iowa Academy of Sciences, Iowa City Meeting. 
