410 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



full generation later that out of them, in Britain, Murchison, Sedg- 

 wick and Lonsdale resolved the Silurian, Cambrian and De- 

 vonian systems, titles which still hold today. 



The analogy established by Nuttall between the general Carbonic 

 section of Iowa-land and of the upper Mississippi valley and that 

 of northern England is one of far-reaching consequence. Its great 

 significance is pointed out by Owen a couple of decades later. Its 

 historic value grows with the advancing years. It is one of the im- 

 portant geological discoveries in America. 



These early interpretations were the means of actually and cor- 

 rectly determining the true positions and the biotic relations of the 

 Carbonic rocks of the continental interior a half century before their 

 geologic age was otherwise generally admitted. These Mississip- 

 pian limestones, as the rocks are now designated, remain today as 

 compact and as sharply delimited a sequence of geologic terranes as 

 they appeared when first recognized in that memorable summer of 

 1809. 



DISCOVERY OF AMERICAN CRETACIC DEPOSITS 



Credit for another shrewd guess in world-wide correlation is to 

 be ascribed to Nuttall. On a second trip on western waters, in 1810, 

 he ascended the Missouri river to the Mandan villages, near the 

 Big Bend, where Bismark, North Dakota, now stands. This voyage 

 was made in company with John Bradbury, a Scotch naturalist. 

 Especial mention is made of the Omaha Indian settlement situated 

 below the mouth of the Big Sioux river. 



A short distance upstream from the Omaha tepees Nuttall exam- 

 ined strata exposed in the bluffs which by means partly of the fos- 

 sils and partly of lithologic resemblance he was inclined to refer 

 to the Chalk Division of the Floetzgebirge, or Secondary rocks, of 

 northern France and southern England.^ So utterly dumfounded 

 was this observing naturalist at finding real chalk so far from home 

 that he hardly believed his own senses ; and he entered into prolix 

 argument in support of his determinations, yet remained to the last 

 somewhat skeptical as to the correctness of his conclusions. 



This is the earliest definite recognition of beds of Cretacic age 

 in America. It precedes by a decade and a half the separation, by 

 John Finch, of the newer Secondary rocks from the Tertiary sec- 

 tion in the Atlantic states ; and Lardner Vanuxem's and Samuel 

 Morton's references of the same deposits to the Cretaceous age. 

 Thus, also, is another great succession of one of our main geologic 



'Jour. Acad. Nat. Scl. Philadelphia, Vol. II, pt. 1, p. 25. 1821. 



