84 The American Geologist. August, i89i 
pretation of the geological structure by Eaton, in 1824, and fol- 
lowed by Emmons in 1856." (p. 528.) 
The discoveries made in various localities bj- different workers 
are referred to in some detail, and the geological is followed l)}- an 
account of the palenotological investigation. In this review men- 
tion is made of the different genera and species described between 
1844 and 1890. Fossils from the Olenellus zone were not found 
in Europe until 18G8, when Nathorst recorded them from Sweden. 
Since that date they have been found in Norway, Russia and Great 
Britian. 
In establishing the limits of the Olenellus zone, the base is con- 
sidered l\v Mr. Walcott to be "where the genus Olenellus, or the 
fauna usuall}' accompanying it first appears ; beneath that horizon, 
the strata are referred to some of the pre- Cambrian groups of 
rocks." (p. 549.) This reference is made irrespective of whether 
the latter lie conformably beneath or separated by a marked strati- 
graphic break. In the former case, however, Mr. Walcott con- 
siders that possibh' the range of the Olenellus fauna, and therefore 
the Lower Cambrian zone ma}- be extended downward into what 
are now regarded by him as Algonkian rocks. Descriptions and 
illustrations of sections in Nevada, Utah, British Columbia, the 
Grand Canon of Arizona, eastern New York, Vermont and New- 
foundland are given in this connection, 
An important and interesting section of the paper is that which 
deals with the features of the North American continent during 
Lower Cambrain time. It is considered that the continent was 
then outlined in a rough way, and had a somewhat similar form to 
that at present. The fauna lived on both the east and west sides 
of the continent. " Strictly- speaking, " he says, "the fauna did 
not live upon the outer shore facing the ocean, but on the shores 
of interior seas, straits or lagoons that occupied the intervals be- 
tween the several ridges that rose from the continental platform 
east and west of the main continental land surface of the time. " 
The idea here expressed will, if accepted, make it necessary to add 
a new map to the series illustrating the growth of North America ; 
and it will have to be represented as of much greater extent than 
the Silurian which came later. The view advanced is considered 
sustained b}' the following evidence : (1.) The strata containing 
the Olenellus fauna are known onl}- in the eastern and western por- 
portions of the continent; (2.) as far as known the Lower Cam- 
brian strata are absent in the interior of the continent ; (8. ) the 
