204 The American Geologist. March, 1892 
The division of the Cambrian into Lower, Middle and Upper is ad- 
hered to throughout the volume, and the country is divided into four 
great provinces as follows: The Atlantic Coast or Eastern Border; the 
Appalachian; the Rocky Mountain or Western Border; and the Interior 
Continental or Central. Under each one of these heads is given a his- 
torical review of the literature pertaining to it; and it is followed in each 
case by a notice of the paleontology, This serves as an index to the 
species described from various localities and by different authors. 
The recognition of the Cambrian as a separate and distinct geological 
system or group is of quite recent origin. Most of the early writers who 
described rocks now referred to the Cambrian placed them in almost 
every system but that one. The Potsdam (St. Croix horizon) now the 
Upper Cambrian, was long considered to be the base of the Lower Silur- 
ian. The age of the Braintree, Massachusetts, beds (Middle Cambrian) 
was not known until about 1857, when the identification of Paradoxides 
from there caused them to be referred to the Primordial of Barrande, 
below the Potsdam. These beds were then supposed to be the oldest on 
the continent, and they were regarded as Lower Cambrian until 1888 
when Mr. Walcott observed in Newfoundland rocks containing a similar 
assemblage of fossils above a zone with Olenellus. It was only then that 
in America the actual sequence of the Cambrian formations was settled, 
bringing about an agreement with the earlier determinations of the Scan- 
dinavian geologists. _It is easy to see that the study of the group is in its 
infancy. 
These facts have rendered it difficult to arrange the material in a con- 
venient form for reference, and have made it nearly impossible to pre- 
sent any detailed study of correlation. We find, therefore, that the bul- 
letin is a history of the literature of the Cambrian rocks in America, and 
the great number of problems still awaiting solution (covering eleven 
pages of the bulletin), serve to show how much remains to be done be- 
fore a full knowledge of the group is obtained. 
In the synopsis of the group (p. 359) it is said that the Cambrian is 
firmly established by the presence of 6,000 feet of limestone and 10,000 
feet of quartzite in the Rocky Mountain region; by over 12,000 feet of 
quartzites, shales, slates and limestones in the Appalachian region; by a 
continental distribution and a characteristic, highly differentiated fauna. 
This is followed by a table giving the typical exposures of the Upper, 
Middle and Lower Cambrian and the rocks correlated with them. In 
substance it is as follows: 
Type. Correlations. 
Adirondacks (N. Y Ste 
Dutchess Co. (N. 
Marble Belt (Vt.) 
Knox Shales (Tenn.) 
Counasauga (Ga. and Ala.) 
St. Croix (Miss. Valley.) 
Tonto (Arizona. ) 
Katemcy (Texas.) 
Hamburg (Nevada.) 
Gallatin (Montana. ) 
_ Belle Isle (Labrador. ) 
| 
| 
UPPER 
: | Potsdam 
CAMBRIAN. 
a 
