MODERN GEOLOGY IN AMERICA 
5 
sively separated from one another were yet jumbled together un¬ 
der the title of the Transition Group. It was not until a full gen¬ 
eration later that out of them, in Britain, Murchison, Sedgwick, 
and Lonsdale resolved the Silurian, Cambrian and Devonian sys¬ 
tems, titles which hold to our day. 
The analogy established by Nuttall between the general Carbonic 
section of lowa-land and of the Upper Mississippi Valley and 
that of the north of England was one of far-reaching consequences. 
Its great significance was clearly pointed out by Owen a score of 
years later. Its historic value grew with the advancing years. It 
was one of the important geological discoveries in America. 
Not only were the Carbonic rocks recognized for the first time 
in the Western Hemisphere in Iowa, but the great Cretacic section 
of chalks and clays was also. Full credit for this other shrewd 
guess in world-wide correlation was ascribable to Nuttall. On a 
second journey over western waters, in 1810, he ascended the 
Missouri River to the Mandan Villages, near the Big Bend, where 
Bismarck, North Dakota, now stands. This voyage was made in 
company with John Bradbury, a Scotch naturalist, who after¬ 
wards for many years resided in St. Louis. Special note was 
made of the Omaha Indian settlements situated below the mouth 
of the Big Sioux River. 
A short distance upstream from the Omaha tepees Nuttall ex¬ 
amined some strata exposed in the bluffs which by means of the 
fossils partly, and partly of the lithologic resemblances, he was 
inclined to refer to the Chalk Division of the Floetzgebirge, or 
Secondary rocks, of northern France and southern England. So 
completely 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 somewhat skeptical to the last as to 
the correctness of his conclusions. 
This was the earliest definite recognition of the formations of the 
Cretacic age in America. It preceded by a decade and a half the 
separation by John Finch, of the newer Secondary rocks from the 
Tertiary section in the Atlantic sea-board states, and also Lardner 
Vanuxem’s and Samuel Morton’s references of the same deposits 
to the Cretaceous age. Thus, also, was another great succession 
of one of our main geologic periods discovered in a then remote 
