78 



LIMESTONES 



OF RED CEDAR, 



more than sixty or seventy feet ; while the depth of the Old Red Sandstone of Great 

 Britain is said, at certain localities, to equal the elevation of Mount Etna above the 

 sea, reaching from ten to eleven thousand feet. Its average thickness, in the 

 British Islands, is laid down, by some authors, at about half that amount. 



In the northern part of Iowa these limestones are seldom seen, by reason of the 

 extensive drift, except in the deep cuts of the streams, and then only in low mural 

 exposures, an example of which is shown in the middle ground of this landscape, 

 looking over the extensive prairies in the Valley of Shell Rock, one of the eastern 

 branches of the head waters of Cedar River. 



LIMESTONES OF SHELL ROCK, CEDAE VALLEY. 



SECTION II. 



ITS PALAEONTOLOGY. 



Pal/Eontologically, the limestones of this period, in Cedar and Iowa Valleys, 

 may be divided into 



1. Lower coralline beds ; 



2. Shell beds ; and 



3. Upper coralloid limestone. 



The beds containing the greatest abundance of Brachiopodes being included be- 

 tween beds charged with fossil corals: of which coral beds the lower is so complete 



