CHAPTER II. 



FORMATION OF CEDAR, AND PART OF LOWER IOWA RIVER, BELONGING 



TO THE DEVONIAN PERIOD. 



SECTION I. 



ITS LITIIOLOGICAL CHARACTER. 



The rocks referable to this age, as they occur in Iowa, are mostly calcareous 

 strata of great purity. Many of its beds are light-coloured limestones, of close tex- 

 ture, and flat, conchoidal fracture, approaching in structure to some of the litho- 

 graphic limestones of Europe. Other beds are limestones of similar texture, but 

 rugged and concretionary viewed in mass ; and often reticulated with thin veins of 

 chert and sulphate of lime. 



Interstratified with these are beds, more schistose, of argillaceous and marly 

 limestones. 



These rocks of Iowa differ, therefore, essentially in their lithological character 

 from the contemporaneous great sandstone deposits, which, in Scotland, flank the 

 southern slope of the Grampians, and encompass that portion of the eastern and 

 western coast which lies to the north of the Friths of Forth and Clyde, as w T ell as 

 the northern coast of Sutherland and Caithness ; while in England they occupy; in 

 Devonshire, so large an area, as to have derived their usual appellation from that 

 county, for the name of Devonian rocks now usually displaces that, formerly em- 

 ployed, of Old Red Sandstone. 



So far as this formation is exposed in Iowa, no true sandstones have been ob- 

 served in it,* not even of a few inches in thickness ; while, in Great Britain, red 

 sandstones, highly charged with oxide of iron, make up the principal portion of the 

 formation. 



The contrast in thickness in the two formations is equally remarkable. Nowhere 

 in Iowa have I found an exposed connected section of these limestones measuring 



* The sandstones which sometimes lie in close proximity to the limestones here spoken of, appear to 

 be of carboniferous date. 



